Please can someone tell me why I can't access certain sites

I have honestly tried everything I can think of.

The background is at the beginning of last winter, our modem died and then linksys decided our router had died. We bought a new modem, linksys sent us a new router, setting up my network was HORRIBLE because I needed to set up static IPs and I have having a heck of a time doing that, but finally right before Christmas, I got everything going.

Then I noticed that there are some websites I cannot access. Among them are walmart.com, photobucket, ingdirect.com, bhg.com and several others.

I cannot access these sites using Firefox or IE (I use version 7). I cannot access them on the desktop or the laptops, mine or DH's. I used to be able to access them on the Wii, but not anymore. I cannot access them at my parents home on their network, but I CAN access them if I bring my laptop to work and use that unsecured network.

Things I have tired
-turning everything off and turning it back on again (has happened MANY times since December)
-downloading new java software
-downloading new browser software(firefox and also redownloading IE)
-downloading new security software...I have spybot, adaware and avg. I have run and rerun scans and the desktops and laptops and nothing is showing any major infection.
-to go along with that I even took it to best buy and they ran their own scan which also turned up nothing. Then they told me that it would be $200to run an "advanced diagnostic and repair" which I declined.
-I have reset all the security settings on the desktops and the laptops to their lowest possible settings
-I have set them all to the highest
-I have reset my router completely
-I have tried a systems restore-this actually worked, for about 30 seconds. I have no idea why it worked or how to make it work again. I did this on the laptop. I haven't done it on the desktop.
I am sure there are other things, but I can't remember what else I have done...