Computer fixing question.?

I’m planning to start fixing computers’ hardware and software problems. I’m not planning to make a company, just smt on my own. I’m not rich so I will not use originall software. Is that going to be illegal? I mean, i’ll not take money for the software, but for the favor.

10x in advance
What if i install downloaded OS and install trial versions software? Is that going to be illegal again?

10x again. I don’t want to mess up with the authorities…
Missed to mention – i will use the S/N from the box i’ll be required to fix.

I don’t know how it happened; one day I got home from work and signed in to a bunch of pages of advertisement being displayed. I tried using Avast, Search and Destroy and 1 Click Maintenance to no avail. Search and Destroy actually deleted something important to the registry and my icons and start button and bar wouldn’t display anymore. I had to load it up in safemode and undo everything it cleaned up, which fixed that problem but the malware still remains.

One thing I did notice is that normally my windows updates are automatic and now it is turned off and I can’t turn it back on again. Another thing is that these are all trial versions of the anti-virus and malware detection/elimination software. I’m at a loss though, usually I can get this cleaned up in a jiffy but this one seems to be serious. System Restore doesn’t have a mark to where I can restore it to an earlier time either.

Any ideas?
I would just wipe it clean but of course I can’t find my XP disk at all.

Is there any place online where I can download a full version of a registry cleaner, because all I can find is trial versions and those only fix like 5 problems. Is there a way that I can fix errors on my computer without having to download and install one of those softwares?

where can I get a registry cleaner that cleans my registry ? I don’t want one of those trial versions. I want to be able to down load and use my cleaner.

Where can I find a good free registry cleaner online and not the try before you buy or trial versions?