100% CPU on multiple OSes

 Hi,

I have an XPS m1330 that is two years old.

I had the motherboard replaced due to the standard faulty GPU about a year ago by Dell.

The CPU now frequently reaches 100% usage and the system slows to a crawl. The fan is of course going pretty hard (but not as hard as it could?)

Different programs show up from time to time as using the CPU time in the resource monitor.

I have of course scanned the system for both viruses and malware.

I was running Vista when it first happened. A few months ago I installed Windows 7. Same thing there, happened about half an hour after I installed Windows 7.

Since last week it basically always happens. I just ran a boot CD of Ubuntu, and the same thing happens there. Both cores at 100%.

I ran the Dell diagnostics (system and memory), and it does not find any errors.

Anyone have any idea?

Thanks,

Mats