Don't waste your money on GeekSquad. They are awful. I found a guy in my town with good reviews and he did OK but that didn't help much.
There's some good websites like bleepingcomputer.
If you have Macafee, remove it. It's worse than a virus. And Windows has pretty decent built in antivirus now. Every computer I have ever had that had Macafee gradually slowed down until it became unusable. Removing Macafee helped a lot.
If you know how to look at which processes are running, see if one of them is taking up all your memory or CPU. Then google whether it's a necessary proecess, malware, or what.
That's all I've got. I have completely given up on several old computers over the years and just went out and bought new ones. By the time you pay someone $100 to "fix" it, you could pay a little more and get something brand new.