|So if nothing happens when you turn on the PC how are you able to use it? |
Have you opened the case and looked at anything? Your description could indicate a number of possible causes.
Failing power supply
Failing hard drive
Corrupt Windows installation (this issue is likely to exist but is probably caused by repeated boot failures)
Hardware and fans full of dust/ dirt, causing overheating.
Solution to the fourth cause is to blow out everything using canned or compressed air. Be sure to blow out the power supply from both ends too. DO NOT use a vacuum cleaner. You can kill your system from static discharge.
Another thing you can do that cost nothing is to re-seat all cards, RAM and cabling, one by one. Snap the RAM in and out 4 or 5 times each to burnish the contacts. Be sure to fully seat the RAM and expansion cards, if any are present.