Connected to Internet but no web pages

Hi, I hope someone can help me with my internet mystery.  I have a Dell Vostro 200 desktop computer.  It was new in August 2008 and runs on Windows XP Service Pack 3.  It has a Core2Duo processor and 2Mb of RAM.  It’s connected via an ethernet cable to a Linksys Wireless-N router, which is then connected to my HughesNet (satellite) modem.

I’ve never had any trouble with it and have been very pleased with it – until a few days ago!  I worked on the internet for about four hours, paying bills and posting some ads on craigslist.  Then I turned off the computer and went out to dinner.  When I turned the computer back on six hours later, I was surprised by the slow internet connection.  I could not get any web pages to come up – just progress messages saying, “waiting for www……”.  I could not even do a speed test because I couldn’t get on the 2wire web page.  I tried and tried in three browsers – Google Chrome, Mozilla Firefox, and Opera (Internet Explorer quit working on both of my computers after a Windows Update one day last year).  I rebooted the modem -  I rebooted the computer – no web pages.  After a few hours of frustration, I turned on my new Dell laptop and got onto all my favorite web pages with no problem – and satisfactory speed.

Even though I know that I made no changes to the computer’s configuration that day, I have done the following things – 

(1) I went to Control Panel / Internet Options and restored all the security settings to Default.

(2)  I connected the modem directly to the computer, bypassing the router.

(3)  I ran a virus check of the whole hard drive with Avast.

(4) I ran checks for malware with Spyware Terminator, Malwarebytes, aSquared, and Spybot Search & Destroy.

(5)  Every night I use CCleaner to remove all temp files and clear cache, as well as creating a new restore point before I turn the computer off.  I have tried to restore to several earlier Restore Points but got an error message that nothing was changed and it could not be restored.  

The current situation is –

(a)  My laptop computer has no problem, so I know it’s not the modem, the satellite dish, or the router.

(b) Downloading an update from within the anti-virus and spyware programs presents no problem and seems to be as speedy as usual.

(c) If I reboot the computer and open up one of the browsers, I can download one page from any of my bookmarks, but then I cannot go to another page through any links on that page or through another bookmark – until I reboot the computer again.  And then, I will still only get the first page I click on.

I really need to be able to access the internet from my desktop computer.  I hope someone out there will recognize this problem and offer a suggestion for it’s solution.  

Thank you so much, - - - Vicki in California