Question : Problem: HP pavillion a5040a Desktop - CPU fan constantly on and goes into sleep mode randomly after PSU replacement

I have a customer who reported no power to their 2 year old HP pavillion a5040a desktop PC.
I installed a new PSU, and the machine started fine and booted up to Vista
The only problem was the fan was constantly on and the machine randomly went into sleep mode - sometimes after vista had booted, but sometimes when i tried to enter bios, sometimes after a few seconds sometimes after 10minutes. The machines blue power light on top of the tower turns orange and it will not come out of that mode by pressing any buttons , mouse etc
I have to hard cut the power and reboot - when i do it comes up with vista repair screen because it wasnt shut down properly
I checked the CPU temperature it was 48c
I couldnt see any fan control or sleep mode controls in the bios
not sure what to try next...

Answer : Problem: HP pavillion a5040a Desktop - CPU fan constantly on and goes into sleep mode randomly after PSU replacement

turns out it was PSU - I put a better quality PSU in and the fan returned to normal speed and no more sleep mode
Thanks to everyone for the suggestions and I hope this helps somebody else