my grandma's desktop (dell studio XPS 435 MT) has a graphics card problem that ive been trying to fix for years. the problem is the fact that when i play a game like cities:skylines or euro truck simulator 2 on directx it comes up with triangle shaped holes in the graphics of the game. the main reason why its doing this was due to a experiment i did back when i was still learning how to use a computer. the experiment was to overclock the graphics card and that experiment failed due to the previously mentioned problem ive been trying to fix for years.... i am pretty much stumped because i even asked a computer repairman to see if there was physical damage to the graphics card and even he didn't see any of the sort.... i really need advice and serious help.