If its a monitor issue, try disabling any integrated graphics adapters, or take out any added video cards. Could also be bad memory. Perhaps a cable got knocked loose somewhere as someone else suggested. Only way to find the remedy for your issue is process of elimination.
As far solutions specific to mobo's or heatsinks, I'm not qualified to give a response on that since I've never personally installed or configured either of those 2 items......YET. When and if I ever get to build my own system(and I desperately want to), and I get to work with the said items, than I can post back on how to deal with those issues. But by than you'll have it all worked out
TCM