STOP. Don't worry about Windows modes, if it is that old (6 years) there is many things that can be wrong with it. First can you turn it on and get to BIOS? If not stop there. Open it up clean it out with canned air, paint brush on the vents, fans, etc. all over it. Then look at the parts write them all down (we need a real SPECs list to understand what your working with). If cleaning doesn't work (turn on still can't get to BIOS), does this have a GPU AND onboard video? Did you try onboard video?
At that point I would disassemble the entire computer, all parts. Place the mobo on a piece of wood or cardboard box. Reseat the CPU back in, one stick of RAM, GPU if it doesn't have onboard video, then connect the power switch from the case, then wire the PSU cables to the Mobo. Can you get BIOS? If not then let's test what is/isn't working.
Unplug the RAM, turn on, does it give you the beep pattern that there is a problem with Memory? If not then the Mobo is bad. If it works, then insert the RAM and take out the CPU, does it 'error beep'? If not then the Mobo is bad.
Realistically you would need a compatible computer to test the other parts, but this would be the basic testign.
If this is all over your head, either take the computer to a IT shop for service or dump it and get a console, much easier to maintain.