Computer won’t shutdown

Dear Sirs, my computer will no longer shutdown and all this started to happen after I replaced a DVD player for a new one. I also installed a wireless USB hub for a B Network by Linksys.
Any suggestions? I already reset the BIOS on the motherboard.
At first it would just restart by itself, but now it just hungs at the end where it says that system is shutting down, but it never does it.
Thx for your help