CougAr.
last time it borked the pc and cost money to get it fixed
The step you missed then was,
Anything you’re not sure about, ask.
… though TBH, there was probably something wrong with it to start with.
That’s probably your problem, right there. The free one, presumably? I’d suggest changing it for Microsoft Security Essentials, it’ll run better on an older PC. Before we do that though, I’d recommend making sure you’ve not got anything nasty on there.
Download MBAM, install it, let it update and then run a quick scan. If it finds anything, make sure it saves a log file.
Assuming that’s clean, do an online scan with ESET.
Let us know how you get on.