CPU usage shoots up to 100% and stalls the computer

[Uzza]

When I start up my computer the cpu usage will almost imediatly shoot up to 100%, with explorer.exe and sometimes svchost.exe being the problem.
It takes quite a while before it is back to no usage but then when I start Firefox, it will start to use 100% of the cpu!

I've had problems with explorer.exe taking all the cpu before, but then just when I tab out from a full screen program.

I've tried almost everything, from reinstalling on different harddrives, removing some of my memory sticks, removing my grapics card and running with intigrated, all in vain.

Would be very grateful if anyone could help.

PS. Sorry if this is in the wrong section as I don't know what the exact problem is.

 

[stom]

Sounds daft but... are you fully up to date with patches and have you run a full virus/spyware/malware scan?

 

[Uzza]

Yeah I am, the first thing I do after I format and reinstall is to instal f-prot and adaware and update them. Then I let windows update run and download the patches there.

I've ordered a new motherboard to see if that may be the problem.