First of all, ignore the weird anti-Vista crowd. These are just people who think that it makes them look cool to badmouth something beyond their understanding. Vista is a genuinely excellent operating system that got a bad press because people tried to install it on older systems that barely met the higher minimum system requirements and because some arrogant and loudmouthed kids who thought they were experts in XP suddenly weren't gurus anymore with the very different Vista and they resented it, so it got an unfairly negative viral press. In fact, it is an extremely stable, attractive, easy to use and versatile O/S, and Windows 7 is so very similar to Vista in every way that it should have been called Vista SP1.
Secondly, you are running WAY too many security programs. More is NOT better. It's a miracle that your laptop runs at all with all that garbage on it. ONE suite will do it; two is too many. If you want freeware, Windows Live Security Essentials should meet your needs. If you want to pay a little for something a little bit more whizbang, go down to your local warehouse club and get Norton Internet Security 2011 for $29 or so (for three licenses usually).
A note about Norton. A year after you buy it your license will expire. Renewing it runs $60, so it's better to go back to your warehouse store and just buy new disks.
But you may have a real problem. All kinds of nasty stuff like rootkits could prevent updates, and some of it may not be detectable by any commercial AV programs which can only protect against the things they were designed to protect against. The bad guys are VERY clever and even get around security measures put into place by extremely expert professionals at large corporations and government agencies, so don't think a used computer is safe. You have no way to know what may have gotten into that thing.
Did you wipe and reinstall the O/S on this used computer you bought? You certainly should have, and if you didn't, well, now's the time, the sooner the better. I do trust that you got the original manufacturer's O/S and driver distribution disks with the computer. You did, right? Right? Let's assume you did. If you didn't, well, you didn't get much of a deal even if it was free.
First, save all your data somewhere else -- your DATA, pictures, documents, music, etc., not your programs. External USB hard drives with ASTONISHINGLY large capacities are very cheap these days, but something tells me that your data, unless you have a lot of music and movies, falls within the capacity of a couple DVDs or a USB thumb drive or two. This isn't complicated, although saving E-Mail accounts and saved mail can get tricky.
Second, make sure you've got the distribution disks or installation files and keys for software you've purchased.
Now wipe the thing clean with a utility like Darik's Boot & Nuke (DBAN). This is freeware that that runs from a CD. DON'T RUN IT UNTIL YOU'RE SURE YOU'VE SAVED EVERYTHING YOU WANT TO KEEP.
Next, put the initial distribution disk into the computer and run it. After it completes your computer, aside from any dents and blemishes on the surface, will be like new.
Make sure you have a good internet connection. Wire it up to the router for the next step -- don't try to do it wirelessly.
Now, run Microsoft Update. Reboot. Then run it again. Reboot again. Then run it again. Reboot again. Then run it again. Reboot yet again. Keep running it and rebooting until it tells you that your computer is up to date. It is during this part of the procedures that you will be given the option to install Microsoft Security Essentials -- do it.
Then just reinstall your software (at least the stuff you trust), and copy your data back to the appropriate folders. Voila! This is obviously a hassle and will take a lot of time and work, but I am quite sure your ability to receive and install updates will be restored, and your computer will run much, much, MUCH better.