According to this description of SVCHOST.EXE
http://support.microsoft.com/default.aspx?scid=kb;en-us;250320
It is common for it to load up multiple times to accomodate the request for different services....
"At startup, Svchost.exe checks the services portion of the registry to construct a list of services that it needs to load. There can be multiple instances of Svchost.exe running at the same time."
I'm not seeing where the BIOS fits in here but you want to start with as clean a slate as possible. Faulty memory may have a hand in it. Can you just use the new memory you purchased and temporarily remove the old? Also, I'd Flash the BIOS anyway. Do one thing at a time so you can accurately pin point the culprit. Also, I'm assuming that you have one HD. The new one and that's it...correct?
Good trouble shooting is merely a logical process of elimination.