When I was in college (a very narrow window) I put an ad in the local classifieds for in-home PC service. I would and could do anything, but 98% of the people who called just needed a “tune up” – or an antivirus/antispyware installation and run, plus I’d install TuneUp Utilities demo and run a few of their utilities to get rid of some of the crap.
My rate was $25 per hour with a 2 hour minimum (since I was driving places, it would have been a waste of gas to drive somewhere 40 minutes away just for $25). I believe my rate was quite low, comparably.
Places like Geek Squad and their ilk tend to charge by the service, not by the hour. $60 for SuperOptimization or $168 for MegaUltraCleaningUpgrade whatever. It’s all a scam, and those guys don’t know how to do anything than the one thing they’re trained to do. I preferred to do an hourly rate so it’d be fair, since some jobs could be completed in 2 hours, and some stuff took multiple trips.
Usually I’d tell people if it would be cheaper to buy a new computer than for me to make something usable. Then I tell them that I can help them set up and optimize their new pc… 
Currently, as a side gig, I act as sort of a in-home technology consultant for my sister’s boss, a man of considerable wealth and stature. Besides installing TVs and setting up their network and all their computers, sometimes I go there just to keep their computers (mostly Macs) up and running. Sometimes I go there just to run Software Update on all their macs, because when you’re that rich you don’t want to have to think about even that.
No matter what I’m doing there, I charge $50 per hour. Note that this is double what I charged only a few years ago, but my service is so personalized I think I’m worth it (no way in hell you could find a company who does all the things I do; AV wiring, networking, computer purchasing/setup/maintenance/backup… even stuff like Sonos and setting up new iPods and recommending what product they should get), and they don’t have a problem paying.
If I were striking out on my own, for the general (non-zillionaire) public, I might do $40/hr.
After the 5th or 6th PC tuneup I did while in college, I had the whole routine pretty much streamlined. I kept all the files I needed on a CD and a USB thumb drive (sometimes I’d run into Win98 machines without USB drivers) including (this is very important) the latest definitions for the antivirus AND the antispyware programs I used (you wouldn’t believe how long it can take to download those things over dialup… or on a computer without internet).