Damage to pc after power outage?

I may not be able to answer your question but I have actually experienced a lot of power outage (brownouts, blackouts, and even a point where the whole town became a huge Christmas lights!) and like you, I am planning to get a UPS.

So far, I my PC is not yet broken but I have to say I have some problems here and there which might be related to sudden power loss combined with its old age.

I experience what you described from time to time but it was more apparent on my laptop. Long loading and even an unresponsive explorer will appear if it is too hot or there's a process eating up most of the resources or the combination of booth. Closing and cooling it down before opening it usually fixes this up. On my PC though, it is either a faulty device plugged in (Flash Drive, Externall HDDs, etc) or, like the laptop, resource-eating process which causes this. It rarely does that by itself but if it does, simply plugging the devices off and/or resetting the PC simply does the trick.

Another thing which might be related is it sometimes just doesn't want to open. Lights and Fans are on but no post. The fix is annoying since it varies from from resetting bios settings to dismantling the whole PC and resitting everything (CPU, GPU, Memory) a COUPLE of times before it starts again. And if it does, it will only use half of the memory available even when the BIOS and CPU-Z recognizes both sticks. Then I have to do it all over again.

In addition to those, if the PC is not receiving power, it will reset the BIOS settings even after changing the CMOS battery. I assume the problem lies with the motherboard and might be caused by sudden loss of power from time to time.

The only thing I can think of that can be damaged is the hard drive or at least the file being written. I may corrupt the whole thing or just a file. I haven't seen a corrupted hard drive from this though but corrupted files do happen just like when I was saving a Photoshop project.

Aside from those and probably something minor, I haven't seen any new problems in quite a while and I am glad to say that my PC is still working fine (for the most part) and I am not 100% the power problem is really the cause by it.