Internet barely usable

[DreamDweller]

Hello. I've just (last Thursday) bought an HP Pavilion laptop computer with Windows Vista Home Premium. Now I have a number of problems.

1. Some websites won't be displayed in any browser (I've tried IE7 and Firefox 3). Those include mostly Microsoft sites (like 'support', MSN and 'update') as well as some ordinary ones. It starts loading and after 5 or more minutes I get "page cannot be displayed".
2. I can't use Windows Update. Error code 80072ee2 .
3. Windows Defender won't update either. Or anything that's Windows.

I have uninstalled the default Norton antivirus (thought it might fix the problem, but didn't), since then Windows Firewall won't let me view or change it's settings because of an 'unknown error'. I've installed NOD32 Smart Security instead and disabled the Windows Firewall service (through services.exe or smth), no change. Now I have Kaspersky Internet Security, still nothing better. Turning IE7 'protected mode' off didn't help either.
The 'same' internet connection works perfectly on my desktop PC which is on Windows XP SP2 and has the same antivirus/firewall (KIS) for protection.

Please don't tell me to reinstall my OS, because I just CAN'T. I've spent 3 days just installing my games and copying documents to and from dvds... And I don't have my Vista dvd (even though my OS copy is genuine, it was preinstalled and I wasn't given a dvd at the comp. store, they told me I could make the dvd myself somehow, but i have no clue, I'm new to Vista).
And please don't point to MS support site, because I can't access it :/.

Please help! Pretty please with cream'n'strawberries on top...