For example something like this- http://www.amazon.co.uk/MSI-H61M-P20-G3-Motherboard-Processor-Gigabit/dp/B007BZI9BE/ref=sr_1_5?ie=UTF8&qid=1420901826&sr=8-5&keywords=matx+1155+motherboard
Yeah, I prefer building over prebuilt, but they both have their places. I know that some companies have terrible customer support (Dell) while others (Digital Storm) have great support.
As for the OEM Windows 7, unfortunately you'll have to buy a new copy. There are ways to get around that, but I don't think that is allowed to be discussed on the forum. Microsoft might be willing to re-activate your copy if you just call them up and explain the situation.
Don't worry about the motherboard working or not. The majority of parts work without an issue, you just see a lot more bad reviews on NewEgg and Amazon than good because people are more likely to complain when something doesn't work, than they are to review a product when it does work. Some boards are more reliable (Asus) and some less (Biostar) but there is a fairly good chance you won't have an issue with any part, assuming that you go with a more reliable part.
Thank you so much.I will contact Microsoft then and see what they can do.