How to make laptop power up correctly. Instead of white screen. The lights go on and the PC makes its usual noises but only a white screen.

First of all in this situation check the AC adapter. You can test the output voltage with a voltmeter. If you cannot do that, find a known good AC adapter and use it for testing the laptop. It is possible the laptop appears to be dead because the AC adapter is bad (and the battery is discharged). If you know that the AC adapter is working properly and it outputs correct voltage but the laptop is still dead, most likely you have a power issue on the motherboard (or power board on some laptops) and it has to be replaced.
If you have to replace the AC adapter, make sure you use a correct one. The output voltage must be exactly the same as on the original adapter. The output amperage has to be the same as on the original adapter or higher, but not lower.
Situation 2.

When you plug the AC adapter the power LED and the battery charge LED light up. When you press on the power button the laptop powers up but will not start. There is no video on LCD or external monitor.

If the power LED lights up it indicates that the laptop is getting power from the AC adapter. Most likely there is nothing wrong with the adapter but just in case test it with a voltmeter to make sure the output voltage is correct.
Also try this. Unplug the AC adapter, remove the battery and wait for 1-2 minutes. After that plug the AC adapter ans try starting the laptop again. Sometimes this trick helps.
It also could be a memory related problem. Try reseating the memory module, just remove it from the slot on the motherboard and install it back. Try installing the memory module into the other slot (if it's available). If you have two memory modules installed, try removing them one by one and start the laptop just with one memory module installed.
If the laptop starts fine with one memory module in both slots, but will not start with the second memory module in both slots, the second memory module is faulty. Replace the module.
If the laptop starts fine with both memory modules when they are installed in the slot A, but will not start with both memory modules installed in the slot B, the slot B is faulty and you'll have to replace the motherboard or use only one memory slot.
Situation 3.

When you press on the power button, the laptop makes a series or short and long beeps and will not start up. There is no video on the screen.

In this situation test the memory module as I described in the situation2. Try installing a known good memory module. Most likely you are getting a beep error because of a faulty memory.
Situation 4.

You start the laptop. It sounds like the laptop is booting normally (hard drive LED is flashing) but there is no video on the screen

In this situation test the laptop with an external monitor. If the external screen works fine but there is no video on the laptop LCD, most likely there is a problem inside the laptop display assembly. Go to my previous post witch covers laptop video problems in more details.
Situation 5.

You start the laptop and it starts making repetitive clicking noise or grinding noise.

Most likely you hear this noise because of a faulty hard drive. You can remove the hard drive and start the laptop without it. If the noise is gone, the hard drive is your problem. Replace it.
If the laptop makes clicking or grinding noises and you still have video on the screen, you can run a hard drive test utility. I usually use Hitachi's drive fitness test. This test is reliable and easy to use.
Situation 6.

The laptop boots into Windows ans works for a while, but after that it shuts down by itself without any reason or warning. You restart the laptop but the same problem appears again

Most likely it's a heat related issue. Listen for the cooling fan, make sure it works.
Also this problem might appear because of a faulty memory module, try some tips from the situation 2.
The laptop still boots ans you still can see the screen, so you can run the memory test. I usually use Memtest86+. Run the memory test and if it fails, replace the faulty module.

If your laptop is making all the usual noises but has a black screen try pulling the power adapter out and battery then hold down the power button for 30 seconds, plug in the main adapter again and turn it on.
"fingers crossed"

Laptops do not fair well if liquid was spilt, and it does not take much. Remove main battery and turn on, if okay! battery needs to be replaced, next remove ram one at a time and power up making sure you always have one in the laptop, last! hook a spare monitor to the video output usually on the back, if okay! the LCD on the laptop has a bad inverter board, or defective backlight behind the LCD. Now if both show the same symptom it is the Video Graphics Card usually built into the motherboard.

Clicking sound is usually a bad Hard drive. Take the Hard drive out and power it up to see if the noise stops. The fan makes a different noise when it fails.

If I could be of further assistance, let me know. If this helps or solves the issue, please rate it and give a testimonial for my response. Happy Holidays!

Thanks, Joe

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309

Make sure that you are using the correct AC Adapter. Dell usually supplies two different ones. They look very much the same. The difference is the amps. One is meant to be used in their port replicator. Look in the BIOS and make sure you have the setting correct for charging the unit.

Shoot it... Or give a little more information... ^.^.
USUALLY, this is power supply related. If a PS is not working, or not working correctly, your machine will fail to start. If you hear fans and see yellow lights, but no green lights, that usually means the Power supply's CPU-power is not working within acceptable limits. If there are no lights and fans whatsoever, that usually means the ps is toast. But, just to be sure, make certain that the little red switch on the back is set to 115 instead of 230.
If you see a start-up screen (something that says SONY or VIAO when you turn it on) that means that you could have a faulty hard drive, or faulty memory. Your best option is call Sony or let a pc tech give it a look-see. Without more information, I can only make general suggestions.
If you DO decide to shoot it, make sure you do it ONLY during computer-hunting season, and make sure you have a license to hunt computers. ^.^

problably data-cable of LCD has contact problems or is broken. Consult someone with experience in opening the Display. DIY only if experienced, since you can make a $40 repair a $400 repair accidantly ... ;-)

can you access the bios if so reset to default and restart if you cant start up to as far as you can get then try a soft boot (ctl,alt,del all together at once) failing this you could try insert system disk and try to reboot and see if it try to install new copy.if you can get to any of these positions you can reset bios by unplugging and reconnecting rtc,this requires dismantling laptop,i may have service repair manual for your pc ,have to check

Could you explain more in detail what the problem is, what laptop do you have?

Thanks