I think you can return anything bought online within 7 days of receipt under the Distance Selling Regulations, whether it is faulty or not. However, the OS change kind of confuses which date is relevant. Normally, if you want to return a pc or component, you have to get an RMA number from the supplier first, giving your reasons for return. Who did you buy it from? Is it 64 bit Windows 7? No point going back to Vista (a slow dog) or XP (great, but getting near pensionable age soon) so perhaps the best thing to do is sort out the Windows & software (compatibility?) issues.