Monitor dislaying "entering power save mode" when I switch on my desktop

Hi

When I switch on my Pc it says entering power save mode, howwever it does still switch on accept it is very slow and I get a black screen for a long time before a normal desktop appears.

My Pc is Dell studio 540, on windows vista.  I just reinstalled windows vista using the operating system disk, as the factory image restore would not work (which is what I wanted to do initially, but the user guide instructions would not match with the options on the pc for rebooting.

Please can you help me with this as I dont want it to get worse, I reinstalled everything so I dont understand why its still giving problems.

Thankyou in advance.