Well, not much to work with here, but the obvious thing to check for would be the videocard drivers
. Maybe uninstall and reinstall, run dxdiag
and see if it reports anything amiss.
Does your friend know when this first started happening, and what changes were made to software/hardware just before that?
If videocard drivers check out OK, then a /sfc scannow
from an administrative command window may help. If that doesn't improve anything, then a repair install which will completely reinstall Windows but leave your existing files alone.