Nsis, corrupt and installation errors (Multiple Pc's)

I have researched and researched this matter and I have tried numerous attempts at fixing this problem.

Friday I attempted to download a patch to update The Sims 3. I kept receiving a CRC error and .dll file doesn't match. I uninstalled and attempted to reinstall thus receiving a NSIS error. I purchased the Sim 3 base game through the EA download manager which is why I didn't try to just redownload from a disc because I only have the World Adventures disc. I unistalled it and loaded it back up via EA Download manager, still a no go. I removed the EA Download Manager, thinking that maybe this was the issue but the game wouldn't run without it so I had to reinstall, thus receiving the a corrupt file error. I did a system recovery hoping that maybe something I installed the week prior (MS Office upgrade to 2010 and Photoshop CS5) was the issue. To no avail but then that set my Norton back so I attempted to update it and my Norton will not update. I then assumed it was my PC and did a system recovery. Well needless to say I'm having the same issue and on top of that I cannot download anything that I had on my pc previous to the recovery. I receive a executable file error, corrupt file error, installation failed error, etc.

Now here is the kicker, I researched and researched and saw some say they had the same issue and it was the network, the router and some mention possibly the modem. So I just thought I'd try to see if any of the other computer had issues. They all do. I cannot install and downloads from the internet, I cannot update nor can I simply run .exe files. I've even tried to save to my desktop and run from there, no go.

We have three PC's each running diff OS. Windows XP, Vista x64 and Windows 7 x32. I have contacted Time Warner Cable and the rep insisted that he highly doubted it was the router and the modem looked good. They didn't show they were blocking anything. I've run hijackthis, virus scans in safemode, out of safemode, spybot search and destroy and nothing fixes this. We do not use IE browser.

Any suggestions would be highly appreciated. Sorry for this being so long, I just wanted to cover any questions that may be asked.