Your Windows should be brought up to current maintenance levels - at LEAST Service Pack 1, prior to installation of X2a.
Beginning with the X2a release, there is a minimum level of maintenance required for Windows 7, and that is that you must have Service Pack 1 installed. Sonar X2a is reliant on redistributable C++ files that are part of the Service Pack 1 update for Windows.
So, try getting all of the Windows maintenance done, then do your X2a install.
Bob Bone