Problem with Nvidia Go 7600

Hi everyone, this is my first post here so I hope someone can help me!
I`ve just bought a new laptop in Japan - its a generic brand from Mouse Computer ( http://www.mouse-jp.co.jp/m-book/mbp/0705/p530s.html). It has 2GB of ram, the 1.66 Ghz Core2Duo processor and a 256MB(dedicated) Nvidia go 7600 graphics card. However, I ran the 3dmark06 to get a very disapointing score of around 900 (expecting around 2000). My Windows vista experience (vista ultimate) index score is around 3.6 (3d graphics)- again very disapointing (expecting 4.6).
I went back to the shop about a month ago and found the same computer with only 1gb of ram scored 4.4 so I sent my computer back to them. It comes back 3 weeks later and they say theres nothing wrong with it. I took my computer back to the shop yesterday and the computer I ran the test on has now gone, but they have one more the same - however - this one had a score of 3.4, leaving me looking rather silly trying to explain in broken japanese that theres something wrong with mine!
Just to add some more detail about the problem, Ive found that if I switch off the computer for a while and switch it back on, I manage to get the score up to 4.5!! I start a graphics intensive program up - great frame rates for about 30 seconds and then it drops right off, and doesnt go back up again.
Ive tried installing different drivers eg the 101.41 and updating drivers using windows, but I get the same thing, so Im not sure its a driver problem.
Im really lost as to what to do now.
What do people think the problem is - a driver/software problem? Device overheating - (Clock is set to manufacturers settings of 450(core)/350 although N-tune recommended turning one of those down by around 15 or so - I cant remember if it was core or memory. I could not, however, change the clock settings using n-tune)? Another problem? Has anyone else experienced this kind of problem with their notebook graphics card?
Any suggestions would be greatly appreciated.
Thanks in advance for your help.

 

I think your computer might be stuck in powersaving mode.

 

Thanks for the reply. Im not sure how I would check that. Any ideas how I would switch that off? Im running the computer with the AC lead connected and I have all the power save settings in vista set to best performance.

 

Thanks for the reply! Im not sure how Id check that. Any idea how I would change the powersave setting? In vista, I have all my powersave settings set to best performance.