Weird reboot problem

[manveruppd]

Suddenly, last night, my computer forgot how to reboot itself! It now shuts down and automatically powers back up whenever I want to reboot it. This happens both when I use "restart" through Windows, and when I do "save changes and reboot" through the CMOS, so i assume it's a BIOS rather than an OS problem - but I scoured through the BIOS setup menu and I couldn't find a single thing that has changed, so I'm stumped!

Can anyone help me? frequent power-ups and power-downs can't be good for my PSU!

Mobo is a Gigabyte DS3 on the F11 BIOS, OS is XP Pro SP2.

 

[manveruppd]

Any clues at all? I've been through the BIOS setup inside and out and I still can't find what's changed!

 

[manveruppd]

No, no, I meant it doesn't do a warm reboot: every time I restart (whether from the BIOS setup or from inside Windows), it powers down completely and switches itself on again immediately instead of rebooting normally.

Don't see how it can be a corrupted BIOS since I hadn't actually touched it at all around the time it started happening, but I'll give reflashing it a go.