Hello Elaydeful and welcome to the forums
It is possible to download Windows 7 however this is illegal
Not only do the forum rules state that I can't send you links, but you never really know what you're downloading when it isn't an official source. For example, it could be a modified version of Windows laced with malware.
The only thing I can think of is to borrow a disc off a friend or family member and install it using that - but use your serial. It has
to be the same version and architecture though! You need a Windows 7 Ultimate x64 disc, nothing else