lost video input to monitor

You have mentioned neither the thermal numbers on your video graphics device, nor the condition of your power supply, either of which can create exactly the symptom you refer to, and is common enough that a thorough Google or Yahoo search would turn those two up.  A hot GPU, caused by either excessive lint collection in the cooler shroud, a failing fan, poor air circulation within the case, or incorrect application of thermal paste, will shut itself down to avoid burning out. 

PSUs get hot and lose efficiency over time, faster for high-rate, high output units.  If filled with lint, they stop delivering adequate power, and the GPU tends to be the one unit drawing the very most, so when there's not enough juice to it, then it stops working.  PSUs lose about 10% of capacity a year for moderate size units, somewhat more than that for those in the 700 to 900 Watt range.