Need to Identify and Remove a Possible Virus

Hello I am new here. I've been trying to get help with something that maiy be a virus, it's quarenteened in TDSSkiller, BUT I didn't know I had the virus or whatever it is till recently, it didn't show up in my AV reports, but it's in the logs. Not knowing I had it, I've backed up files and copied files to another machine, now theyi might be infected too. One machine has win 7 the other xp home, the xp machine was taken offline and lent to a friend who doesn't use the net. Some backups got put there, on an external drive, and possibly a thumb drive. I tried joining the site that has TDSSkiller and had trouble for some reason, it stressed me out too much I gave up and I came here, there's no one to help me and I may've infected a friend's machine I was trying to fix. My patience for tech stuff is very bad, I'm not a geek and never will be. I gave up on microsoft I can't afford their fees, it took them a week to fix a security problem, (no charge), put me through a WEEK of hell I hope never to repeat, my isp who provides the AV wasn't much help either. Their security program detected the thing, couldn't clean it, then I found the log in TDSSkiller and saw it was quarentined, I tried looking up the thing to see what it is so I know what damage it can do. I am so exhausted, ready to quit the net. I hope someone can help me please, I don't know how this thing got in or how to keep it out, maybe the firewall will, I don't know; an important file is infected and I may need it. If I can't get rid of it I will just quit the net. I'm very careful online, security is my first concern, I do my best, am careful where I go, what I click, etc. I've been online since about '96. Thanks for any help you can offer.