If you are having trouble with your Dell 5150 loading games or programs and running normally, then slowing down, then speeding up again etc...
it may be due to overheating.

Mine was having this problem, i have now called Dell and they are replacing the heatsink and fan. I however still have to purchase and use Condensed Air spray monthly to keep the dust off the heatsink in future.

The following website and threads explain the issue and give solutions.

http://forums.us.dell.com/supportforums/board/message?board.id=insp_general&message.id=139712

http://forums.us.dell.com/supportforums/board/message?board.id=insp_general&message.id=112325

http://www.geocities.com/i5100dustproblem/main/solution.html

I am a little annoyed that Dell locked the forum posts and do not have any information on this issue on their forums or website. It would have cut down my search time considerably.

Hope this helps someone in the same situation i was.

Cheers and good computing

Ian