Corrupt Downloads/Programs on One computer of Network

Good Afternoon Geeks!!

I have been trying to fix one of my comptuers and I have replaced the MB and Reinstalled Windows and replaced the Memory. Now when I try to download AVG/Spybot/Office it says that the file is corrupt, I have tried to download the Office 07 Free trial from Microsoft and it says something to the matter that I must turn off the DMZ on my Router, I have disconnected the router and ran the line directly to the modem. I have rebooted into safemode, i have ran the TCP/IP from speedguide.net, but I still get corrupt files. I have Ran the scandisk and not found any errors on the hd. I have not done any updates to the comptuer, it is a BRAND NEW FRESH install of windows as of about 2am today. I can take the same program and bring it down stairs and it works fine on my old junky computer. I can use a CD/DVD to try and install and it still gives me the corrupt error.

Im banging my head against my desk here....Anyone have any suggestions????



Btw I downloaded HJT as the RUN option and it installed and when i ran the software it didnt find anything.