Windows. I attempted to use remote desktop to log into my PC while I was at the library yesterday, but it didn't work properly. Then when I got home I found that it had somehow completely fucked up my PC so badly that it wouldn't even log on at first. I managed to get it mostly working again pretty quickly, but my desktop background was completely broken, and I couldn't access any of my encrypted files. And system restore wouldn't work, because it wanted to move those encrypted files around but couldn't.
I ended up staying up all night trying to fix it, eventually managed it just now by loading up a Linux live cd and using it to move every encrypted file on my PC to a different drive, then running system restore, then copying all the files back again. Took me ages, and was a real pain in the arse.