My laptop started having a problem today as following:

I'm able to boot windows, log on and all the system/porgrams start normally. works in idle mode. After a while, if i start either playing games/surfing/watching a movie the screen black's out. The system seems to still be running in the background with sound etc still going.
It seens as if it can keep on running forever if i dont touch it... Apparently also works with stuff like music only(wamp)

It seems to me that something about my grapics card fried? i had the computer running 10+ yesterday but its notlike i havent had my computer running for several days.. =/

Hardware Specifics:
Acer Aspire 1690 (bought summer 2005)
1.8ghz - ati mobility radeon x700 - 1gb ram - ...

Any way to narrow down the cause of problem or any way to solve would be welcome
greetz & thx in advance
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edit:
It seems to work fine if i have the laptop running onbattery. even movies and progs worked. but just a few seconds after i plugged inpower it blacked out again...

Does the battery charge normally? Are the power/sleep/screen saver settings correct?

Battery seems to recharge normally...and sleep/standby settings are just as usual....didnt change anything there
when the monitor jus turns blck it seems to just loose signal and backlight switches off too. I tried with another screen attached to the laptop because i thought it was my laptop screen but they both go out at the same time - the other lcd would just say no signal"" -_-

Ok d310n9,
The graphics chip on the motherboard might need to be resoldered. Not many repair shops will do this. They may require that you to buy another motherboard

well...ended up going to the shop since the screen decided to not even turn on anymore...think i totally fried something.
the shop called me back and said something on the motherboard was broken..guess they ment something connecting mobo and graphics...yeah..its gonna cost me around 1100 chinese currency...about 146 usd...
thx for the replies, much apprechiated
keep up the great work

Good luck d310n9,
The US repair price $146 is a fair price for this repair