This problem has bugged me for a long time now and it developed into a serious one yesterday due to which I was not even able to update Tech Salsa.
However I solved this problem myself today and since then it is working absolutely fine without any restarting problems.
Causes of this problem:
1. The first thing to watch out for is the RAM. Since it is the first thing that works while booting, it can be a major cause for the problem.
2. Any recent Hardware change. If you have recently replaced any hardware of the computer then you should get it replaced again.
3. Corrupt Windows. This problem can also be caused if your Windows is corrupt, then just format the system and your problem will go away.
4. Faulty component on the Motherboard. The problem can be definitely caused if any of your components is damaged on the motherboard (see your manufacturer).
I would suggest you to do the following (this is how I fixed my problem)
• Take your CPU out and remove the side lid.
• Reverse Vacuum (blow out all the dust) the motherboard, SMPS fan and everything there.
• Carefully remove and re-insert the all the wires that you can like those of Hard Disk, CD Rom, Motherboard etc.
• Re-insert the RAM after cleaning it and the slot.
• Replace/re-insert the Battery on the motherboard as well.
This solved my problem, hope it does for you as well.