Connection good, pages won't render

Working my way through the revised cleaning process, but if anyone can norrow the scope where I should be concentrating, I'd appreciate it.
Running XP SP2 and Firefox 1.5 & IE6.
Was on the road last week, and suddenly could not connect to any Internet source (cable or wireless). Went through tech support with the hotel provider and determined the connection was good (pings sent and returned data), but it was like I had no connection (page not found errors).
The conference tech guys had me do a restore point back a week, which cleared the problem (their boss is getting a gushing letter next week). They hoped that would clear the source as well (updated and ran Spybot--no detection), but apparently not since the behavior started again last night (seems to trigger on Thursday nights, but I've only got two data points on that).
Another restore has me back online again, but I'd prefer to know what I'm dealing with if anyone has a clue. Don't know how to describe the problem more briefly, so the searching is turning up all application and real connection errors.

 

I am. You rock. Thanks very much.

 

Think so. Got the latest update from Zone Alarm installed, which is supposed to completly address the issue, and the patch from MS. MS recommends backing up before installing SP 3 & I'm so doing that before I hit the go button. If it recurrs, I'll adjust ZoneAlarm and see if that's the cause (that update initially come through the day I was traveling, so the timing was perfect for me to miss it). Again, thank you.