Not a lot of info to go on there, but the basics would be to pull all the fuses (except main one) and turn the ignition on. If the main fuse doesn't blow then one of the other fused circuits is to blame. Put in the fuses one at a time until you get a blow and then you will know where to look further.
Other questions you need to ask, like was the bike running before you bought it? Does the main fuse only blow when you press the starter button (if so, dodgy starter or shorted feed wire to the solenoid). Try running a heavy wire direct from the battery to the starter terminal (just tip the wire to the terminal for a second) and see if the starter works.
Like I said, you didn't give a lot of info and I could go on until I run out of space in the message box. Try the suggestions above and get back to us later.
This sounds like a problem I just fixed. I had power to everything but the starter. My problem was the solenoid. Rap it with a small hammer or something and see if that fixes it. If it keeps doing the same problem. You'll have to replace it. There is a place one wire here and one wire there test but it hard to explain it.
My main fuse nemisis was my cigarette lighter. Bought the wrong lighter and when I plugged it in....pop goes the fuse. If your daring.....replace the fuse with light gage speaker wire. It will hold out better than a fuse, but will still burn out if it is a serious short. I know guys that have done this to trouble shoot, including myself, but I advise caution, cause I don't want to be reponsible for burning up your bike.
Idjit9, it would be nice to get some feedback on the suggestions I've given you already on the Backyard Built board. Electrical problems are definately a process of elimination and trial and error troubleshooting. We can spend a lot of time guessing but you'll never get the problem solved by just asking questions. Go out and try some of the things we've suggested, let us know what you've triedand we'll try to help you in a step by step way.