I bought an Antec 620 HCG. Installed it just now and was able to load intensity 13 without the reset. I have tried to find this info all over the net without success, so hopefully this helps some people with the same problem:

Basically if you upgrade your card on an old system and the power supply can't handle it you will insta-reset, your computer will shut down or restart. The card must be drawing too much power and needs a better power supply.

Let me know if this helped you.