CPU Usage abnormally high, sometimes peaks to 100% for no reason.

So this morning everything was fine, my CPU usage was at its normal 20% or so, occasionally up to 40 if I was playing games or something.

After coming home this evening however, turning it on again was taking much longer than usual. It took about 15-20 minutes to get to the desktop, and another 5 to load the icons properly (probably because I have Skype set to run automatically on startup).

When it finally worked with enough speed for me to actually do anything I checked my task managers performance screen, and it was up around the 90% area, and then hit 100% and I experienced the same immense slowness with everything.

I do get periods where my laptop is usable, but even then my CPU usage varies wildly between 30% and 80%, with the only stability coming aroudn 50-60% mark.

I am currently running an anti virus scan (I use ESET NOD32 Antivirus 5) which is almost complete, but I doubt that it will help - has anyone got any clue how to fix this?

My laptop is a HP Probook, model number P4510sVP7570Q5X320NIBNCN32Wa. I run Windows 7 Home Premium 32bit on an Intel Core 2 Duo processor, roughly 2.26 GHz.

None of them, the largest one is my web browser at 300,000-400,000K.

Thats why I said no reason lol - its not any program I'm running, the CPU usage just spikes massively without anything being done.

Anti Virus scan complete, cleaned a few things here and there but hasn't solved the problem.

Right now it seems to have got better for a bit, but I don't hold out hope that it is a permanent recovery - I will check that next time it happens and post.