Crate tube amp will not power up but cooling fan tries to run

If this happens only when the guitar is plugged in, most likely there are two possibilities. The first, you have some issues with the electronics in the guitar OR are using an acoustic guitar witch has an extremely sensitive pickup that provides nothing but feedback. If this is happening with the guitar unplugged, there is a mountain of possibilities.

A vacuum tube tester is used to test tubes. Years ago, you could walk into an electronics store like radio shack and test your tubes. I suggest you take the amp to good music shop that repairs amps. They will be able to test the tubes.

Possible that the output tubes that were replaced are drawing too much current, hence the popping sound (may be "motorboating", one common word to describe a similar sound)

This means the tubes need to be biased properly. You need to get it to someone who knows what they are doing, ie a good amp tech, not GC. The voltages here are dangerous.

First thing would be try another guitar with the amp. This will eliminate if it's a problem with the guitar or the amp itself. If the guitar is working properly then check all the tubes to be sure they are all seated into there slots completely. Depending on how much use they have been played it may be a good suggestion to then replace your tube's. Occationally the tubes will start loosing power, making sound fluctuate up and down or distortion sounding static in background noise. You will notice a big difference with newer tube. But remember the bias must be set correctly to match the new tubes so they won't over heat. You can check out youtube for setting the bias. Anyway this is my suggestion and I wish you good luck.

I don't know how you know the tubes are good... It is possible they are microphonic... try tapping them with a pencil (only need to worry about the smaller ones).
Beyond this look for cracked circuit board or bad solder... especially near the control pot leads. This is a common problem. Look for cracks near the booard mounting points.

Check for bad tube... it HAPPENS that brand new ones fail... USUALLY if they last 50 hours, they will last for the expected life. The bad tube would likely NOT be the main power tubes, as the amp would still run on one cylinder...

Start easy. You could have a bad power switch. Do you get any kind of indication of any life at all, like tube filiments or front panel indicators? If the fuse is blown you have a fault that is drawing excess current, in which case you can check the rectifiers that create your bias voltages, yank the output tubes to see if they have an internal short, less likely would be a shorted filter capacitor (although I have seen it). You could also have a bias problem on the output tubes that causes them to draw excess current and likely makes the tube(s) glow bright red before popping the fuse. If this is the case, look for shorted or leaky coupling capacitors and burned bias resistors, or maybe just a tube with internal shorts, and you will likely have junk tubes as a bonus (they don't take kindly to glowing bright red- meaning a glow that is far more intense than the soft glow of the filiments). If the fix gets more involved than all of this, give me your email addy and we can get hard core.

Your amplifier is a solid-state rectified tube amplifier. This means that a tube is NOT used for the power supply. Why is this significant? Because most of the time you have the problem you are describing, it is because of the tube rectifier.
Since this amp does not have a tube rectifier, the problem is likely one or more of the tubes. I have seen in 95% of the amps I repaired that the tubes were the cause, and since the amp is so new, I would suspect tubes first.
Now the hard part: which tube? Without a tube tester, you will have to use the 'firewall' technique. You will need to get a bunch of replacement fuses, as you might go through a few untill you find the problem. Radio Shack is a great place for fuses (make sure they are SLOW BLOW type).
The problem is almost guarenteed to be the power tubes: they are a big failure mode in tube amps (the preamp tubes are not as likely the problem).

This is what I do at a customer site without a tube tester:
(1) Have either a KNOWN TO BE GOOD REPLACEMENT SET OF TUBES or a NEW SET OF TUBES.
(2) Have plenty of fuses.
(3) Start with power tubes: they cause most of these problems. Replace burned out fuse.
(4) Replace all 2 (or 4 in your case) with the good tubes.
(5) Turn on amp and play on it (30 minutes at various volumes and settings). Turn it on and off many times using the on/off procedure your amp requires (like using the standby switch on some models).

* if the amp plays and works, likely you had a bad power tube. If you are blowing fuses, the problem is either the power amp circuitry or the preamp tubes.

* Leave the good power tubes in before going on to the next step. Also: the minor difference in bias wont matter for what we are doing now: the bias being WAY out is almost never the cause.

(6) Check preamp tubes (easy to do, as this does not require us to poke around on the insides).
(7) Replace burned out fuse (atleast number two by this point).
(8) Replace all preamp tubes.
(9) Turn on and repeat step 5.

* Blowing fuses at this point means atleast two types of repairs needed: retention tube sockets or someone to look inside the amp. Either way, this is a serviceman repair (things I do). Since the amp is so new, take the warentee buyout and throw it back to where you got it. Crate is real good about dealing with these issues (if you are the only owner and it is within warantee).

If you need to contact warantee support, you can tell them you have had the amp re-tubed and the problem still persists (meaning they can brush you off with 'just get it retubed and then call us if there is problems'. This is like 'take two asprins and call me in the morning: 95% of all tube amp problems can be fixed by this (retube, not asprins).

If you have to do the warantee route, KEEP YOUR NEW TUBES. The preamp tubes are fine, but the power tubes may be damaged. Wait for what Crate tells you before you use them. This is if you are cheap. I would pitch all of the tubes and consider the 70 bucks as my cheap attempt to bet I am in the 95% solution number (tubes are the cause). Otherwise, the repair will cost shipping at a minumum. Dont you love it: tube amps are expensive and require someone with deep pockets to enjoy the tone. But what can we do: tubes DO sound better and when everything is working, they perform reasonably well.

Good luck on this!
-mike

Ah yes: complete catastrophe. Usually when everything is not working, it is a single reason and when that single reason is fixed, so is the amp.

Based on what you tell me, I am going to say you have a bad power tube. And I will even go as far to say that you buy a set of tubes and play on them as long as you can. If so, then you not only burned up the tube, but weakened the power section and may have a slooow tube frier. I always tell customers: modern tubes have an effective life of less that 1200 or so hours and that varies. Replace the tubes once per year if you gig with the amp: period. Otherwise, guys like me (doing repairs) stay busy and the tube companies get rich selling tubes to amps with weakened power sections.
It sounds like you burned a power tube and blew a fuse. First, you need a new set of power tubes and some extra fuses (go to Radio Shack and set the value you need in SLOW BLOW fuses).
Then, replace all the power tubes. Don't worry about biasing yet, we are just seeing if there is a problem. Next, replace the fuse.
Turn on the amp and play on it at various volumes and settings. If all is well, take the amp to a tech and get it rebiased. If you can afford it, pay to have the grid/plate and other resistors changed so the power section will be like new (clean slate with new tubes). Your amp will love you for it.
Almost all of the amps I have worked on for performance problems (cant keep tubes to stay alive for very long) are directly related to end user use. When you use a tube until it blows it ALWAYS TAKES SOMETHING WITH THE TUBE WHEN IT GOES (like the power section components). The compents will be weakened and the tubes will 'wear' at different rates that can even move them out of the 20% tolerence they must be within to sound good. 99% of the time a board repair with a retube after a catastrophe fixes the amp until the next time it is 'run into the ground'. Tube amps are NOT invinceble: they are weak compared to solid state and expensive to own. But we love tubes because they sound great. I have solid state to knock around on, when when it counts, I play only with tubes. I have spent hundreds on good tubes because you do get what you pay for.

Hope this helps!
-mike