easy lads, lets not getting him spending unecessary money, its seems someone has been messing with your video settings.
I think you can solve this one by booting into safe mode..
Start up the pc and after the post screen does its memory check keep tapping F8 until a menu screen comes up
select safe mode
let it boot (may take a while longer than normal)
once its fully loaded right click somewhere in the middle of the screen and select display properties.
Then go to the settings tab and click advanced, next click the monitor tab
here should be a box marked monitor settings and in it a drop down box for refresh rate
under here make sure the box is ticked that says "hide modes this monitor cannot display"
It should leave you with a couple of option in the drop down box, select a fairly low Hz value and select apply.
Now restart the computer and hopefully you will be able to boot up into windows normally.
I think thats the right way to go about it, someone will correct me if not
