so now i bought myself a new pc and i had a windows 7 retaill cd lying around and i installed it but then it asked for the key and ive used my key up already on another pc and i still wanted to install windows so ive entered the key and the install got finished. and after some time i wanted to instal new windows 7 and the oem is more cheap so the question is can i install windows 7 home premium oem over my current windows 7 (unactivated) ?? and i also had ubuntu 12.11 on my pc
You don't have to re install.
If it's windows 7 home on both. regardless of retail or OEM. They are the same the only difference is the product key. So just enter your OEM product key on the pc you want it on.
Keep in mind, you may only have your retail key installed on 1 machine at 1 time.
Having it on more then one is a breach in the terms of service and could end up blacklisting your product key.