I've not looked at the actual site, but I am an HCI-type-guy.
A really good book to read is
Don't Make Me Think! its subtitle is something like, "effective web design."
It's
the definitive work in this area. Pick it up, read it through a couple times, then look at your site with renewed vision.
Okay, now I've looked at the site.
The picture at the top is confusing (and fish-eyed) and the layout is cumbersome.
The "About Us" page needs MAJOR work. Writing in the first-person is frowned upon, and as soon as you bring up
Just because I am so young doesn't mean that I can't do for you what a major company could do at a much more fair price.
a customer connects that to the earlier "basement" comment, connects the dots, and will bail.
Also, the "About Me" section will work against you. Unfortunately, these kinds of things (bio-sketches) really only work in psychology/psychiatry, journalism, and academia (where it's permitted by the journal).
I think your fee schedule ($100 flat-fee) will get you in trouble. For instance, were I evil and competing against you, I'd take my machine to you. What I'd not tell you is that I've cut one pin off the HDD connector, made an intermittent short between the motherboard and case, and done a few other nasty things. You'd spin your wheels for maybe a day and get backed up. I, on the other hand, would be free to turn 10 normal systems around (as I'd be there for your overflow). All it would cost me is $100. You should also put a bottom cap on the amount you'd be paid. If you don't, and you re-seat RAM for me and then want to charge $60 on-site, then I'm going to pro-rate it, give you your $1, and tell you to sue me for the rest if you think you have earned your $60.
Finally, I do have a bit of advice for you as far as an appropriate toolkit, as I'm sure you don't have all the bits and pieces:
- XX-piece computer repair kit (you likely have).
- Torx screwdriver bits, specifically T8, T5, T10, T15.
- Anti-static (grounding) wrist-strap.
- Test code reader / POST-test card. These are expensive, but nothing's cooler and faster!
- Compressed air.
- Screws, fasteners, motherboard standoffs, paper washers, etc.
- Band-aids, Nu-Skin, and other medical gear. Some cheap cases are SHARP. People don't like blood on their carpet.

More specs and pictures.
I'm confused about your special of the day. Specifically, as Windows XP with valid license is about $
Almost as much as the special, I don't see how it's possible to make money on the deal. If you are *ahem* eliminating the cost of a Windows license (which I don't think is the case), I'd advise against it (MS and the SBA
really go after small businesses much more so than individuals.
Also, if you're doing business, you'll need a business license (about $20 or so) and maybe a zoning certificate/petition to conduct business in your parents' home (about $5-$20). I've done both, and it's a matter of filling in forms and taking them down to the city.
I think we've covered this ground before, but it came up above. I myself have my own domain name through GoDaddy, and my hosting is done through HostGator. I've not had issue, and I'm a pretty technical guy.
