Check your brake lines where they bend in line with the wheel rims themselves. I would be willing to bet a cold one that one of your brake lines is worn through from being rubbed by the rim. Happened to mine.
Brake systems are Fairly simple in design. Master cylinder, line(s), caliper. Your problem is in one of these areas.
1. Inspect your system for leaks, any fluid spray, etc
2. Pressure wash your machine thoroughly - so you can see what the hell you are doing! Put on stand (or something) and take of your front rims!
3. Check your pads - any lide left? are they running up against the brake rotor like they should be?
4. Fill the master cylinder reservoir (sounds like you did) with DOT 3 or what ever your manual says, I use DOT 4 myself - be sure you get the rubber piece back in there correctly and it is in good shape!
5. Open bleed screws - 1 at a time and make sure you get fluid to come out by pumping lever. Then re close.
6. Refill master cylinder if needed
7. Check brake pads are they up against the rotors, can you get them to stop the rotor if spun? Are your pins that hold the pads on clean? They should be lubed every once in a while also.
8. Bleed the system of all air adding fluid as necessary. If they don't start to work you have a leaky seal or line
9. Make sure the brake line is tight to calipers and master cylinder.
10. If you caliper pistons are leaking or a seal is bad you should see some fluid coming out by now somewhere. If it is not building any pressure you will have to disassemble some of the system to find the problem - I would start with the master cylinder.
Hopefully you have fixed or located you problem by now