3DMark03 Crashes, but not 3DMark2001?

As some of you may know...I got this cheap 9600Pro (and it is cheap with its 3.3ns memory )
Anyway..I tried to test my pc's stability with the Heatsink that i've installed. It can run 3Dmark2001SE for more than 3 hours without any crashing (loop 30times+), but when it runs 3DMark03, it randomly crashes..., sometimes long, sometimes short, it would just freeze at some point...I'm wondering why? even at stock speed 400/300, it might crash as well.
Should I be aware of it? I went on Futuremark's website, it <A HREF="http://service.futuremark.com/servlet/Index?pageid=/support/search&cid=9&fid=1216" target="_new">says</A> that 3DMark is designed for a single benchmark run, but that doesn't explain why it would crash for a few hour.

I clocked it at 425/303 when I ran both 3DMark
Any thought?

I've just tried Catalyst5.8, same thing, system crashes.
Sth interesting, I discovered that not only 3DMark03 crashes, but 2001 crashes as well. But like I said, sometimes it can go up to 3h, sometimes it goes only up to about 1h10min.
When it freezes,
1. sometimes it freezes while looping.
2. sometimes I see an error msg popup by Windows saying that this program has problem and need to be closed by Windows etc etc, then Windows freezes. Odd, when this happens, num lock or caps lock still respond, I can still open Windows Manager, but once it appears, nth moves, I can close it with ALT+F4. Things would appear, but nth moves in screen.
3. more often, screen is just all blue, with resolution 640x480, nth in screen, nth respond.

I read the Event Viewer, I found out sth weird.
My computer always freezes after 2 Events:
for example:
Type_Date_Time_Source_Category_Event_User

Error______31/08/2005/_1:51:38PM_System Error_____(102)_1003_N/a
Information_31/08/2005/_1:50:54PM_Application popup_None_26_N/A
Information_31/08/2005/_1:50:54PM_Application popup_None_26_N/A


I checked those Application popup, I found this:

Application popup: : Machine Check: Regs
Application popup: : Machine Check:

After googled a little bit, I found some information.
It's the MCA(Machine Check Archicteure) that is working, but I don't understand why would my pc crashes within 1min after MCA starts.
I found ppl says that by disabling MCA, the problem will be fixed, but that doesn't sound good to me.

I'm kinda running out of idea.
If I didn't install the heatsink properly, 3DMark wouldn't go up to 3h right?
I'll try a last few thing, such as running the 9600 at stock speed 398/297(594), and disabling MCA.
Any thoughts will be appreciated!

Athlon XP 2700+@ 2.17GHz
Abit NF7
Crucial DDR333 512MB 2/2/2/5
ATI Radeon9600Pro 425/303 w/Catalyst5.8

I think taking it back to stock speeds is good