The computer that used for along time will often damage on its motherboard. This happen because the electronic component on Motherboard in injury time condition. Damaged motherboard are marked by reduced in your computer's performance, restart or shut off suddenly, or very slow not as usually. Or your computer not boot to windows.
To solve this problem you must do some job :
1. Open The computer Case
2. Discharge all cable connection on motherboard
3. Take motherboard out
4. Clean up with paintbrush
5. Check all electrolytic capacitor ( EC )
6. If you see this EC not normally ( puffy, broke, have erupt, etc. ) you must replace it
7. Check all solder condition and repair if needed
8. Be sure that you have finished this job, as well as possible
9. Re-assembling motherboard on the case and try to turn ON your computer
10. Don't forget to check temperature ( via bios )
This an electrolytic capacitor :
and this is some example for the bad electrolytic capacitor :
You must replace it, if you see a like this
I hope this experience will be help you...