Hi there,
If you are getting one short beep from the motherboard it means that everything is OK.
The fan on the CPU won't always start up straight away so you don't need to worry too much about that, unless of course it doesn't start after about 1 minute.
I think it is quite safe for you to power up the PC and let it go through the initial stages of booting. If there is a problem you will soon know about it.
Good luck
ATB