PC Crashed again

My PC crashed again in the Sunday night. First, there are several message about the processes can not rn, and then file missing errors. After restart, system could not start for those missing files. This occurs even after I format the driver C:. But I found there are two bad tracks on the disk, I then use several tools to repaire the disk. When I tried to install the system, Windows setup give error message during file copy, which says file can not be copied, CD error. That's so strange, CD error? I reintall the system several time, this error occured continously, but every time, different files. I borrowed a XP CD to install the system, the error is still there. What's the reason? Maybe some hardware problem. I removed net card and TV card, the error came again. I plug off second harddisk, error again. I pluged off 256DDR RAM, the PC can even not do the self-check, this maybe the problem of memory. Then I pluged off the second 512M RAM, it worked!, the there was no error during the coping of the system files. Nice, at least I could install the system again. There was no more error after reintallation of the new system. Ok, it should be the problem of the memory.

I took the memory back to the PC shop where I bought it, the clerk told me it is not possible to exchange for a new one, because the in-door guarantee is only for 6 month after the deal. The rest guarantee is for send back to the factory. I have to wait 6 weeks to get it back. That's terrible, I have to use the machine again with 256M memory.