Connected to LAN, but no internet

[Ctrap85]

We have a home wireless network, with several laptops and one desktop.  It worked fine for well over a year, but as of Monday, the desktop can no longer access the internet.  It says it is connected to the network.  I tried both IE and Firefox - nothing.  I've tried a number of things, including, among other things, 1)unplugging the modem and router, then powering up again, 2)turning off the desktop and then powering up again, 3)connecting the desktop directly to the modem with an ethernet cable, all to no avail.  Wirelessly, it says it's connected at 54 mbps and connection is excellent.  Hardwired, it says it's connected at 100 mbps.  I use antivirus (Norton), spyware prevention (Spyware Doctor, Spybot Search and Destroy, AdAware) and a firewall (formerly the free ZoneAlarm, which I uninstalled in the last few days and now use the Windows firewall).  I suspect (but I'm just guessing) that the problem may be related to an automatic update of SP3 that was downloading/installing on Sunday, when the internet last worked.  When I went to go on Monday, it didn't work.  Any suggestions?  Thank you.

[Carbon Dudeoxide]

Exactly what is wrong?

Also, if you look in Device Manager, are there any yellow exclamation marks or question marks?

What OS is this?

[Ctrap85]

Thank you for your response.  I'm embarassed to say that the problem and solution were somewhat obvious.  Despite the fact that, under System Properties, it indicated that I was running Service Pack 2, enough of Service Pack 3 had been downloaded/installed to mess things up.  I checked under Add or Remove Programs, and SP3 was there.  I removed SP3 and was able to access the internet.  I then installed SP3 without any problems.

[Carbon Dudeoxide]

So problem solved by uninstalling SP3?