Problem installing software on newly built pc


Just helped my housemate build a new gaming computer and we've hit a problem. We've got it booting up with Windows 7 Ultimate 64bit but have a slight problem installing certain software on it. Tried installing Google Chrome, Itunes64bit and various anti-viruses such as avast, avg and sophos. It is possible to install stuff on it, for example Steam, Firefox and Microsoft Office work perfectly on it. Anyone got any hints?

If needed, these are the specs i can remember:

Mobo: Gigabyte G41M-ES2L
Processor: Pentium E5400

Have to ask him about the rest but he's gone to the pub to drown his sorrows.
Can you describe "a slight problem"?

That's like if I said "My car has a specific issue when I try and use it. Fix it?"
Basically, none of the software will install. I think it's mainly software that has a downloader in it like Chrome and iTunes.