Hello kind Geeks, 
I'm kinda out of ideas with how my PC restarts randomly. So here's the history.
Lightning struck the road 3 houses from us. (It was really like Kakashi's Raikiri xd
) We felt the ground shake and my PC shut down. After a painstaking isolation, damaged components were the power supply, and the motherboard. Intact were processor (AMD athlon 64 kinda old, really), 2-1GB memory cards (DDR2), and ATI Radeon 512MB video card (PC's 2 years old, xd
)..
So I bought a new power supply, of course, and a new motherboard. Not really high spec'd, just MSI740. Hard drive was okay but I wanted to have a bigger space so I bought a new one that's 320GB.
Now, the problems are:
1. Any browsers (IE, MFF, GC) would crash dwn randomly. Especially if I turn on User's Customization for NB Profiles.
Other instances is when I already have like more than 3 windows open.
2. If I have browsers, and other files open, say excel, word, PC restarts at no particular reason.
3. If my 9-yr old bro plays crossfire, the PC restarts when he finishes up a mission, or when in the middle of the game.
4. What's worse is we could not install his WOW game lest the installation would reach 99% and stops due to a disk error (as per its prompt message).
I tried reinstalling the OS, reformatting the drive and I feel that these aren't helpful nor are they even relevant to the issue. I'm suspecting it must have something to do with the Memory. Or could it be the new hard drive?
Thank you for your advise.

I'm kinda out of ideas with how my PC restarts randomly. So here's the history.
Lightning struck the road 3 houses from us. (It was really like Kakashi's Raikiri xd
So I bought a new power supply, of course, and a new motherboard. Not really high spec'd, just MSI740. Hard drive was okay but I wanted to have a bigger space so I bought a new one that's 320GB.
Now, the problems are:
1. Any browsers (IE, MFF, GC) would crash dwn randomly. Especially if I turn on User's Customization for NB Profiles.
2. If I have browsers, and other files open, say excel, word, PC restarts at no particular reason.
3. If my 9-yr old bro plays crossfire, the PC restarts when he finishes up a mission, or when in the middle of the game.
4. What's worse is we could not install his WOW game lest the installation would reach 99% and stops due to a disk error (as per its prompt message).
I tried reinstalling the OS, reformatting the drive and I feel that these aren't helpful nor are they even relevant to the issue. I'm suspecting it must have something to do with the Memory. Or could it be the new hard drive?
Thank you for your advise.