imac g5 shutting off

hello mac forums... i have a imac g5 1.8, 2gb of ram with leopard..lately its been shutting off mostly during startups and when waking up from sleep, the screen flickers on startup dim to bright and the bluetooth doesnt load either most of the time.the bluetooth has been a issue since ive had it . 1 year ago i replaced the power supply and think the new power supply is on its way out..the question i have is how to make sure it is the power supply again and if so what options do i have..i changed power preferences to restart in case of a power failure and it will restart instead of just shutting off..ive been reading about g5s having power supply issues. any help is appreciated.

well you could do a hardware test with your leopard discs, this would tell you whether anything else is faulty.