There have been countless times where people tell me they have a virus and once I sit down at their computer to check out what's going on, it ends up being a general Windows error, missing.dll file, multiple installations of adware, etc..
There is an almost unlimited number of scenarios that could be your issue. It would be impossible for me to cover all non-hardware problems in this guide, but I would like to cover some basic things that I've always done when someone gives me a computer to work on.
This is stuff everyone should know and I hope it helps you out. I've found it almost less likely to come across a legitimate virus than something more simple, though I have removed thousands of really nasty viruses over the years.
With that said, let's quickly talk about what you should do first...