Don't worry about version 1.1. Install version 3.5 (I believe this is the latest version) Service Pack 1. I installed it on a friend's PC with W7 a few days back with no issues.
He probably wants it for a few software, for example a few facial recognition software require .net 1.147~ which is ridiculous since you can't down grade.
Anyways what is the error because we're in the dark here. For all we know it could be a battery error, compatibility issue, or a bunny jumped into your computer.
Hi , you've exactly encountered the same problem as of mine. Go to the link and follow the instruction step by step. I did it and it worked !Good luck!