Please Help! My pc wont power down

Any thoughts on this one?
Just upgraded my pc
Motherboard-Intel D925xecv2
Processor-P4 3.73 Ghz EE
Memory- 1 Gig ram (2x512MB ddr2 running dual channel)
Graphics Card-Msi 6600GT 128mb
Hard Drives- 2x 200Gig running in Raid.
Cdrom Drive
Cd Burner
Floppy
Xp Pro installed and SP2

The problem i am having is once the pc has been on for a while (it seems)
When i go to shut down, the o/s seems to shutdown fine, monitor goes to standby, but the pc carries on running....???
This problem happens 90% of the time, I Have swapped my QTec 400 w power supply for another 400w (old Supply) but no change..... I Have also removed all devices (USB).....but still no luck........
The power readings seem fine and I have checked all connections to the board...all drivers seem up to date......
Has any one else experienced this problem...? the only way to shut down power is to hold the power button in.
There are no error logs.....so i assume xp has shutdown ok
Please Help

Thanks
gary

Go to start\settings\control panel\power options and make sure the settings are OK, then report back.

and get a proper PSU, QTec or Old Power supply is not right for your kit, you have spent lots on it, at least spend enough for a decent PSU, look for Thermaltakes, excellent performance for the buck.

m@

i had ths problem after installing Logitech software for my new mouse. uninstalled the software and it was fine.

sounds like your system is set to go into standby or hibernate rather than power down? control panel > power options...make sure its set correctly.. :devilish:

check the standby mode in the bios - most likely set to S1 standby, rather than S3

Well thanks to you all, The cure was a 525 Watt Hiper Power Supply..............Used the machine at least 10 times on new PSU and no problems.........
Thanks again
Gary

A valuable lesson learnt in getting a decent PSU. :D

what the hell are you doing turning your PC off in the first place? Switch it back on and do some tweaking/gaming/overclocking/benchmarking at once!!