Are you able to get to Computer>Properties to activate? If so you should be given a phone activation option when Product Key is rejected.
If you only mounted the ISO using PowerISO it was not booted. Did you run an in-place "Upgrade" install which is a Repair Install in Windows 7, or Custom clean install?
Either way it didn't wipe anything so if you have corrupt or infected code it may still be there.
I'd Burn the ISO to DVD using ImgBurn at 4x speed. Then truly boot the DVD (via BIOS) and wipe the HD first, then Custom Install using Drive Options to partition and format.
Here are tips to get a purrfect install based on hundreds done here: re-install windows 7
If you have any further problems after burning DVD, I'd check the HASH
against official Windows 7 hash: Windows 7 RTM SHA-1 hash / checksums
. Here is a link to where MS made good after the Student download didn't provide an ISO at first: Microsoft Fixes Windows 7 Student Edition Upgrade Problems