Systemax ascent won't stay powered on

Verify some connection setting toward the power supply. please test the PSU if is working. if not then, you should examine the PSU for fault. if find fault in the PSU should fix or let the repairman fix it for you. However if you want to repair PSU you can provide a new one in the vendor where your system from.
Please leave comment b 4 you rate for further discussion on the system, thanks, melnavz.

have 256mb systemax ascent. after i boot up windows xp it will operate for a few minutes up to 15 minutes normally and then freeze up on whatever i am doing.

I recommend that you replace the PSU, Power Supply Unit with a new one, this is a simple task. Remove the plug from Motherboard remove the four screws from the PSU at rear and get a replacement one say a 450 Watt job. Install and ya be good to go.