Do I need to replace my PSU?

DifferentlySane

Honorable
Apr 29, 2013
4
0
10,510
Hi all,

Recently, my computer has been restarting itself after I've shut it down. The only way I can get it to stay off is by holding the power button down until it gives up. That was annoying, but now it's getting worse. I'm also occasionally having trouble starting it up. I press the power button and the fans start whirring, but after a few moments, it stops. Then it restarts, and the process repeats. Eventually, it manages to stir itself into life, and after that, works normally. I've had no power issues while the PCs been running, just when starting/shutting down.

I've poked about on the internet for an answer and I suspect my PSU is on the way out, but I'd like to know if this is definitely the case before I fork out for a new one

Some computer stats, in case they help:
Age: 4.5 years
PSU: 600watt Quiet Quad Rail
OS: Windows Vista 64
CPU: Intel Core 2 Quad
Motherboard: AsusTek P5Q Deluxe
Memory: 4GB
BIOS: AMI 1702
SMBIOS: 2.5

Any suggestions?