Monitor goes blank when OCing

[TheMostWantedPolishTwin]

I have a JUICB TBred 1700+ that I've been running at 1800-1900 MHz for like 2 years, on my AOpen KT266A mobo, at stock voltage, with stock HSF - getting really good temps. Recently I got Abit NF7 rev. 1.0 hoping for better OC. After clearing the CMOS it booted just fine.. installed XP, started OCing. Tried 1900 MHz first..booted into windows so I started folding client.. runs fine.. CPU temp around 40 C - I decided to let it go for a while and then try more. But after couple mins the screen goes blank and the led on the monitor turns from green to amber. At this point I have to turn the comp off by holding the power button for couple secs - the reset button doesn't work... it happens even at slower speeds like 1700 MHz.
When I got the mobo I replaced the NB HSF on the mobo with the golden Zalman heatsink.. it doesn't seat very tight - do you think it might be the NB overheating? Help me guys.. I really want to fold with the most MHz I can get...

edit. forgot to mention that upping the CPU voltage even to 1.75 didn't do anything...

 

[TheMostWantedPolishTwin]

I think I figured it out... it seems like my 300W Fortron PSU can't handle this mobo (what's really weird since it should be more than enough..) - I tried it with an off brand 300W and managed to run it stable for 2hrs+ @1750MHz... so I guess this means I need a new PSU...