Computer kicking me off internet?

I have a three year old Compaq Presario and a cable modem. For about a year now, every time I start the computer, an error message reads: 鈥淚nvalid BackWeb Application Id 鈥?940576鈥濃€? This has never really been an issue, but it might have something to do with the numerous problems I鈥檝e been having recently. About a week ago, I noticed my graphics 鈥渇lip鈥? i.e. all the graphics would turn into the safe mode format for a second, and then they would flip back to the normal format. Also, the sound on my computer would randomly stop working. All this would go away after rebooting, only to return later in my session. I downloaded those Microsoft Updates and installed Norton Antivirus. After those two operations, my computer went into a reboot loop, requiring a trip into Best Buy, where they told me that I did not have a virus and that it was probably a software problem, requiring 120 dollars worth of investigating and possibly a wipe of the hard drive. I promptly said goodbye and tried fixing it on my own. My computer was no longer in a reboot loop, so I did a system restore (getting rid of Norton in the process) and a defragment of both the C and D drives. I also re-installed the Microsoft Updates. Then my latest problems came up. A few minutes into my session, I get an error message (besides the one mentioned earlier), saying: 鈥淕eneric Host Process for Win32 Services has encountered a problem and needs to close.鈥?Also, my computer kicks me off the internet 10 minutes into my session. A reboot cures this, only to kick me off the internet after another 10 minutes.