Blank screen but PC keeps running

[Allshevski]

Hi, I've just had some really stange things going on my computer. I left it for night just to do some processing, and when came back to it this morning, monitor was turned off, displaying "No Input". Power led was steady, like it was still turned on. PC was still running, keyboard and mouse had power but HDD led was blinking very rarely. Also, when I put my hand near exhaust fan, the air was colder than sometimes on idle, but I left it under heavy load. I've checked all cables and tried pressing some buttons on my keyboard. Also, pressing power button did nothing. Only forced shut down helped. When I booted it up, everything was normal, no log files, even standard windows startup screen. Also, it's been running for 4 days under continous full load but never failed. And passed Furmark + Prime 95 with max CPU temp. 90°C, but during last days temps were not higher than 60°C on both GPU and CPU. Any ideas what could cause this?