lap-top CPU seems to be getting `throttled'...

I recently purchased a Studio XPS 1640 lap-top from Dell. It was running fine, but now it runs way under par any time I run anything. It runs just fine, but anytime I try to run any `serious' programs or games, it's almost as though the CPU is being `throttled' somehow. I have a CPU meter on my SideBar, and both CPUs go through the roof. I tried playing a game which my lap-top exceeds even the recommended system requirements, and it couldn't even run the game in the game's version of `Safe Mode', with absolutely all of the graphic enhancements turned completely off. 

I didn't install anything or change anything that I'm aware of. I just went to play that game one day, and now it runs everything extremely slow.

I did go to PC-Pitstop to see if I was crazy, but the results definitely show my computer performing wayyy under expectations, but only in some of the areas, which just goes to point-out that there's definitely something wrong... It's very weird.

My lap-top specs:
sys: Dell Studio XPS 1640 lap-top
OS: Windows Vista Home Premium x64 SP1
proc: Intel Core2 Duo 2660Mhz
mem: 4GB
vid: ATI Mobility Radeon HD 3670
HD: 500GB
optical: DVD r/w
screen: 16" 1600x1200
sys rating: 5.5

I tried System Restore, but it didn't work. It only went back a month, tho, and I have no idea this has been going on, because this isn't my main machine, and, like I said, it runs fine. It's only when I go to do something `extensive' that it acts-up.
I have not touched my Registry.

I don't know how to get a "Tech Express" link, but here are some of the more notable rankings from my PC-Pitstop test:

World Portable Rank = Bottom 46%

Pit Score:
CPU: 6127 MIPS - Bottom 32%
RAM: 4097 MB/sec - Bottom 23%
Video: 80 MP/sec - Bottom 23%
3D Video: 1656 fps - Top 3%
Disk: 565 MB/sec - Top 1%
Internet: 565 Kb/sec - Bottom 4%

Pit Rankings:
Processor Clock Speed: Intel Core2 Duo 2660 MHz Top 1%
Memory Installed: 4096 MB - Top 1%
Total Storage Space: 465.61 - top 21%

My CPU only gets a score of 6,127 compared to an average of 10,596 but a Disk Score of 64 compared to an average of 51 among 7 similarly clocked CPUs.

My Video Score is 80 compared to an average of 234, but my 3d Score is 1656 compared to an average of 1112 from 3 other similar video boards.

Hopefully this shows the anomaly I was talking about. My lap-top is ranked really high, but tests very poorly on everything but the 3d Video & Disk it seems.

I've tried watching the system processes, but nothing jumps out at me. The System Idle Process is at the top (of the CPU Usage) most of the time. Then, when I run an application or something, it just seems to eat-up all the CPU for no reason.

Any help would be much appreciated. I miss my fast lap-top! =)

Thank you.

- Jimmy