It is possible the file is too big for your e-mail provider to accept it. But it ought nopt lock up the PC. How big is it ? What is the file extension ?
There are compression programmes on the Net that can reduce the size of a file, but video is notoriously large and so they may not reduce it enough. Also there are other programmes that can split a file into upteen parts and reassemble them again. But I think you may need experience in using that sort of thing.
If size is the problem maybe you'd be better copying it to a DVD and loaning it to your friend ?