PC is not booting Dell Optiplex 100

Are you using a four pin connector( connected to power supply)? if yes it will give you error. Connect the fan as shown in the image

for first ,check power supply
This is one of the most common problems. There are various things that can go wrong, from using the wrong laptop power supply to a faulty power brick or even a blown fuse.
First, make sure the battery has some charge. If you're not sure, and there's no power indicator on the battery itself, then remove it entirely and just use the mains charger.
Check over the wire itself, as power supplies get beaten up, especially if you carry them everywhere. Weak points are at the ends where it joins the black brick and at the plug which connects to the laptop. If you can see the coloured wires inside the black outer protection, it could be time to buy a new PSU.

you seeting your pc's battery option or checked the connection.

if you have two partitions on your hard disk drive that means that D partition is dead! If you have two separeted hard disk drives C and D check the flat and power cables, check the jumpers on hard disks, switch the possitions of the jumpers on drive D to SLAVE position!

power supply problems does it have a separete power supply if so you can try to change or if you have someone with the same you can ask to try it.if its internal power supply it needs to be fixed.

Probably best to return to the shop with the pc and power supply. Possibly a loose connection somewhere or the power supply could be overheating.

Could be the power supply. I would go to an electronics store or computer store and buy a cheap ($10.00) power supply tester. Unplug the main power supply connector and plug it into the tester. If none or only some of the tester LED's light the power supply is bad. If so you have two options; 1) remove the power supply and open it up. Look for a fuse, which could have been cold and cracked causing the filament to burn open. If you do not want to buy a power supply tester you could go directly to check the power supply fuse. 2) Replace the power supply is your second option.

Bummer, but what you describe is ususally some cable dislodged. Remove and reaseat everything and try again. Remove and reseat the ram, leave the processor alone.

There could be two possible faults that could cause a problem like this:

First it could a short on the motherboard at the power supply connecter, which to repair would consist of taking the motherboard out of the laptop, and maybe replacing the power supply socket. It could also be a faulty componant on the motherboards power supply circuitry.

Second it could be the power supply itself, the only way to test this is to aquire a new power supply, you could take the laptop and power supply to your local pc store, explain the problem to them and ask if they could test it with a new power supply, if it works with the new power supply then you can buy it, if it dosent then you know the problem is with the motherboard. hope this helps and please post back the results, thanks.

Choosing a good power supply depends on a few factors; The amount of power your PC and all it's internal/external connected devices need. The way your PC-casing is built (for airflow).

First it's important to know if you have added any internal/external hardware to the pc since you bought it (hard drives, video cards, usb devices, memory etc.). If this is the case then you definitely need to upgrade, but reading the second and third factors I mention below will shed more light on that.

Second (if possible) you need to check the voltage levels on your current Power Supply via you PC's BIOS or by using a program like Speedfan. If any of the voltages show a reading below what they are supposed to deliver, it means you need a higher amperage on your next Power Supply for that particular line. There are three lines to check (12+, 3.3+ and Core voltage). Usually Power Supplies have a Table with voltages on their sides and on the package. Refer to the one of current Power Supply to see how much amperage your new Power Supply needs to have.

Third it's important your new Power Supply has the fans positioned in the right spots. If your always make sure the air is blowing out of the casing. If it has a small fan on the back, it most likely blows outwards (sucking air from inside your PC case though the Power Supply). If it has a big fan on the top side, it's most likely designed to blow out of the top of the PC case. If it has a fan on the bottom side, it's most likely designed to **** air from the inside the PC casing and blow it through the Power Supply. However it may also be designed to blow out the side of smaller PC casings, in which case the Power Supply is position in front of the motherboard.

Fourth is kind of the-rule-of-the-thumb, always (if possible) buy a brand Power Supply. Generic/Standard Power Supplies do not nearly achieve as much power/lifetime/quality as a brand Power Supply. I recommend a Cooler Master, for their silent but powerful coolers.

Fifth but definitely not a lesser one. Check what connections your PC need. Count the amount of pins connected to your motherboard (usually either 20 or 20+4 pins). Most modern Power Supplies cover most of the connection types. But you don't want to come home with a new Power Supply that isn't going to support your old IDE drives or something.

You could help us help you by providing us with a list of Hardware your computer contains. I can search your PC type and read the specifications, but they don't show what you put extra in/on your machine.