My first computer was a Spectravideo SV-318 and I've been doing stuff with computers ever since. I'm familiar with DOS, Windows (3.11, 95, 98, 2000 and XP), Linux and FreeBSD. I've also done 4 years of tertiary education including engineering, computer science, analog and digital electronics.
I don't have any fixed charges, although my wife suggests a $20 minimum isn't unreasonable. I'll work for cash, barter, beer or food. If I can't solve the problem I don't expect payment. If I can answer your questions over the phone I'm happy to do that for free too.
I do this for fun and for a bit of cash. If you're not comfortable with that there's plenty of places you can go for professional support.