Uninstallation Errors & Assorted Problems

To put it plainly something's up with my computer. My post is going to be lengthy but I'm not sure how many of the problems are related...

So a few days ago I was trying to load one of the Sims games. My autoplay has not been working when I insert a CD so I've been doing it manually through the D drive for months. I figured it was the fault of something like Online Armor which asks for approval on EVERYTHING, that it had disabled Autoplay as a safety measure. Sims didn't load so after checking some Sims forums elsewhere online I resolved to uninstall everything Sims related & reload it. I inserted the CD for the base game and clicked my D drive and it said I didn't have permission to access it. I restarted the computer and the base game loaded completely with no other problems. The first expansion pack loaded, the second loaded all the way to 100% then said it was checking for updates. Suddenly it said it couldn't connect and said installation terminated and when all the way from 100% to 0%. Sims forums said to shut down the computer before it uninstalled and the game would still be loaded. It was but the game didn't upload to play. I figured why waste space if it's not going to work? So I tried to uninstall it through Add/Remove programs removed the title on the list but when I checked in the Program Files it was all still there. I tried to use the game's uninstaller but again I "didn't have access". So I tried deleting folder by folder. Then for the one's that wouldn't delete I when inside file by file. Finally between multiple restarts I managed to delete these problem files.

I'm not so worried about the Sims game itself this isn't the place for that I know but after today I've fully realized it's a bigger problem and it's my PC. I thought it might be a malware problem of some sort so I when to the READ & RUN ME FIRST run-down. I've used it before so it wasn't a problem and when to the Windows XP Cleaning post. I wanted to make sure I had the right software in all the proper categories. BOClean was just recently incorporated into Comodo Internet Security. It's a firewall & anti-virus, so to make sure they didn't counteract I disabled the firewall component of Online Armor & planned to uninstall Avira AntiVir. No problem with the firewall but AntiVir again was uninstalled using Add/Remove and seemed alright. Then in Program Files it was still there & in my Start up icons. I have deleted all the AntiVir files except msvcr71.dll & shlext.dll . I stopped the Windows Security Center through the registry thinking that the relationship between Antivir & that were why the files couldn't be accessed and were "in use". It had no effect.

Comodo Internet Security was downloaded from the Comodo website but when the .exe didn't work and made my computer crash. I restarted and deleted that one and I downloaded the .exe again from MajorGeeks. This one didn't appear to work either but after giving it some time I ran through the installer successfully. I did the restart the installer asked for and upon start up error messages came up saying files were missing. It was from Comodo because when I clicked its icon the same messages came up again. I had the same trouble uninstalling Comodo as everything else so I when into safe mode and was able to delete it through there. Back in regular mode the only trace left of Comodo was Security Center which had it listed as the active firewall which added to my decision to stop it thinking it needed to refresh.

Extra Details:
-I used a defragger for the first time today (Diskeeper Lite). It had an error with a "snap-in" but otherwise seemed successful.
-I've run scans with Malwarebytes, Spybot, and a paid edition of SUPERAntiSpyware. I've used CCleaner repeatly.
-I'm using Windows XP SP 3 and my local disk is 71.3 GB with 20.8 GB free.

I'm sorry it's lengthy but I'm not sure how much of it is related so just trying to give all the details I can remember. I don't know how to do much of this myself (the registry stuffs all new to me within this week) so I've been following walkthroughs. I believe in finding your own answers but I've done all the independent research I can and now need a little more personalized help. Any aid anyone can offer is most appreciated!

 

Thank you very much for replying! I was able to get Comodo downloaded with Firewall & Anti-Virus running smoothly. I used CCleaner as instructed to fix all the registry problems. I also downloaded Revo Uninstaller but Avira didn't show up when I tried to delete the remaining files in the Hunter mode. It replies that it can't uninstall it because no installation package is found. I only have two files remaining in the Avira folder shlext.dll & msvcr71.dll . I used it on two other pesky programs in the traditional mode and it worked beautifully. Autoplay still refuses to work as well and appeared to be activated. Again these are minor issues as long as these remaining files aren't a real disturbance.