Slow computer--please keep reading

I know there have been a zillion posts on this subject, and I think I have read them all, but I still need help. Here's what I have on my Dell Inspiron 1526 with Vista Home Premium: SUPERAntiSpyware Free Edition, SpywareBlaster, CCleaner, AusLogics Disk Defrag (all of which I use every Monday), Avast Free Home Edition, Comodo Free, Windows Firewall (don't know why I have both). When my computer slowed down drastically (20 to 75 seconds to load a page, jerky mouse, slow typing), I did a scan with Avast, and then I downloaded MalwareBytes and did a scan with it. No virus, only incidental spyware. Then I removed the last application I had downloaded (a stand-alone reminder program). And things are still the same. The computer was lightning fast when I got it a year ago. What can I do? Thanks.

 

I do not have Comodo's anti-virus activated. My product version number is:3.8.65951.477. After reading plodr's reply but before reading DomLuc's reply, I deactivated the Windows Firewal--no change. Then I deactivated Comodo and surfed to four safe websites, including MajorGeeks--no change. I reactivated Comodo and here I am.

 

Some time ago, I did the things recommended in MG Basic Computer Maintenance Guide. So I set about to do the things mentioned in DomLuc's last post, but decided to update Comodo first. And I got this message: Error 108. Update could not be completed. Please check your Internet connection settings. I don't even remembe what my Internet settings are, or how I get to them. Please help--and also tell me what this is all about.

 

I have done all that has been suggested except for two things: I'm saving the programs check in Control Panel for last because it takes me awhile to check each one I'm not sure about. The other is one I don't know how to go. I saw 'safe' configuration for Windows Services in Vista in the 'Black Viper' guide, but I don't know how to access it. Can you tell me how? Thanks.

 

Success! My computer now seems as fast as it used to be. Except for 'safe' configuration for Windows Services in Vista in the 'Black Viper' guide, which I don't know how to access, I finished up all the suggestions posted on this thread. I only found five programs that I felt comfortable in removing. The computer seemed faster, but not as fast as before. Then I used ccleaner and auslogics disk defrag (the latter said I had over 100 junk files that it recomended I eliminate with their BootSpeed, but that costs money so I didn't do it), then I rebooted. After reboot, things seemed back to normal. Thank you immensely for all your patience and perserverence with me, as well as for all the helpful suggestions and advice.

 

Thanks again. Enjoy.