I recently got a radeon 9700pro graphics card,. and now I'm experiancing lockups 5-15 minutes into playing games, this sint happen immediately after getting the card however, it seemed to crop up later and stay. Also when I restart my computer, or turn it on, the monitor often stays on standby and im not blessed with all the usual booting up sounds, so basically it doesnt start up, after a while of turning the power off, turning pc on it eventually starts up normally (can take dozens of tries through, or sometimes even just 1).

The lockups seem to happen mostly in 3d games.. including half-life, (well natural selection, a mod for it), medievil: total war (the big battles), and some others I forgot.

One of the first things I thought might be the problem was the really really lousy PSU I have in my computer... some 250watt one, I've ordered a new 550watt one which should be on its way in a few days, but until then I'd like to isolate any other possible causes.

my system is a mixture of old and new parts.. so a lot of it is crap... :
1.33ghz tbird
256mb ram
via kt266 mobo
radeon 9700

Another possible cause I thought might be overheating, and if so that situation has been made worse by me unplugging my extra exhaust and case fans in order to get the PC to boot up properly (it seemed to help in that department).
Before this card I had a horrible kyro 2, it didnt lockup like I'm currently getting however, so that does lead me to believe it may be more to do with power than overheating.

also maybe my ram has suddenly gone faulty? it would make sense if it had, at least to me as the timing of these problems cropping up isnt 100% consistent with what i would have thought.

oh one more thing, I am currently using the directx 9 and the new ati drivers that are made to work with it (most recent). but I have had these problems on the old drivers and old directx too.

well, if anyone has any suggestions as to what they think may be wrong and what I can do about it please say.