Hercules ATI 9800 PRO Problem

I recently bought this new card along with some other components and I have a question -

When I have my system running for a while I lose the signal to the monitor. The system still runs but all I have is a black screen, the monitor goes onto standby. It even started doing it during the boot up process. After going through all the steps of booting up the monitor goes into standby just when the user account selection pops on.

I'm hoping this is just a driver problem / Directx problem so has anyone got any ideas please.

My system is as follows :

Asus A78nX - Deluxe motherboard
Hercules ATI 9800 PRO Graphics
1GB PC3200 DDR400 memory
Windows XP Pro

All help is very much appreciated.

It could be the PSU as in it has played up on me before. If I connect a second HDD to the system it does not even boot. It's a 400W PSU, manufacturer unknown....it came with the case. (One thing I noticed just now while checking it has P4 written on the side... 0o)

I have exactly the same card and have noticed it does like going into stand-by but only when left alone for a while...a move of the mouse brings it back to life and on boot it takes a few secs longer than normal to show post screen (usually dont get to see initial post with Proccessor and mem info now. - strange) I have a 350w Antec SmartPower running the system below inc DVD drive + DVD Burner + 2xlarge HDD's + 4xLED Fans + system exhaust. may have something to do with the PSU if its a cheap no name one...have you tried it in another machine or tried unplugging a few devices to give it more power?

<i>Mmmm Dawn AND Eve at the same time...Drroooooll
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<b>XP2800 Barton, 2x512Mb PC2700, ASUS A7N8X, Hercules 9800Pro 128Mb.