Sorry don't know the full spec's but it's a emachine 960 upgraded with a 9800pro (from a geforce 4 mx) plus a gig of ram (from 512), 2gig p4 and 80gig HD.
When this problem first started was soon after the 9800 went in (but soon after not straight after).
Still haven't got round to uninstalling Norton yet!
Try to find out what PSU it has. Since there has been a few upgrades the power requirement has increased and usually the PSU's that come with prebuilt computers don't have much extra wattage.