I have an Asus P7P55D and for the past few months I have been having this problem fairly consistently.
Whenever we lose power and I go to start my computer back up, everything will come on except for the monitor. I turn off the power and unplug everything (All USB devices, the power cables, the monitor, the power strip from the wall, etc...) wait a minute then plug them all back in. This usually works. Sometimes I have to do it twice though.
Here are the rest of my specs:
XFX HD-487A-ZWFC Radeon HD 4870
Antec EarthWatts EA650 650W
Intel Core i5-750
G.SKILL Trident 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 2000
I know everyone's first thought is going to be the power supply, but I never have any other issues except for when I lose power. The PSU is inexpensive, but a solid, no frills performer.
This seems more like a waking issue from Hybrid Sleep (S3 + S4) and compounded with a corruption cause when the S3 (corruption) memory is lost due the outage.
2. Press and Hold the power button - this will restart the (S4) Hibernation file to be 'restarted'. Save any open files and reboot to clear the corruption.
There have been a couple of 'HotFixes' to cause Hybrid Sleep waking issues so make certain Windows is up to date.
You are a little over my head with your explanation of the problem, but I understand that the UPS would solve it. I was just concerned that there is a bigger underlying issue with a major component.
Solution 2 has me a bit confused. Are you saying to hold the power button after I turn the system back on and see that there is no display? That is how I shut it down now when I am in the problem (although I do not start it back up again after that, I start unplugging things first).
Press and Hold the power button + press the power button to restart (if needed).
I've only had that problem with a 'HotFix' and recalled the 'gist' of the solution. IF Press + Hold + Press fails you 'can' press the 'reset' button then the (S4) aka saved to disk state will be lost more than likely.
IF pulling the 'plug' followed after the problem rebooted into to the saved (S4) state i.e. not a fresh restart you in the end accomplished the same thing.
As far as a bigger problem, (NO) especially if the root cause a power loss. Your PC is attempting to 'save' your data prior to sleep and the loss of power messed with that intention. However, I'm pretty anal so whenever I suspect 'corruption' I always run SFC (System File Checker):
Schedule both options and reboot, it takes 30~45 minutes depending on the size/speed of the primary drive: