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.