1980 yamaha xs 850 special

Hi, everyone I'm new to this and just wanted to see if anyone can help me. So i have a yamaha xs 850 and it won't start, i don't even know where to look! It been sitting for a while now and i asked my neighbor, and she let me have it, so far i had replace and check the fuse, haven't yet a new battery, but i use my brother battery to jump and test. Also added gas and tried to kick start it but it won't budge, then i tried the electric start and it won't start either. So what can be the problem?

Thanks in advance,

Dara