Some friggin' weird issues.

Lately, my computer has been having some weird problems, most of them focused around Gmod. Firstly, when I tried to open up Gmod today, my resolution dropped from 1440x900 to 800x600 out of the blue. Nothing else was changed (That I noticed). Then, when I went into SP, my username had changed, to something like Angus513 (Although this symptom has since disappeared). In addition, while I was playing on the Pulsar Effect Lite Roleplay server (208.122.52.35:27015), I crashed because, apparently, I was missing the paintbucket model, and the Error model (models/error.mdl, I think) was missing as well. Now, as far as I know, the Paintbucket model is part of HL2, and should come with Gmod, and the Error really should be part of it. Then, to top it all off, a whole shitload of programs that I’d disabled at startup long ago came back when I rebooted today. So, do any of you know what’s up? I’m already planning a reinstall, and just in case, I’m doing a virus scan.

Thanks for your help.