Brakes - pedal to the metal

I have a '98 Blazer as a 2nd vehicle with 4 wheel disc brakes. Besides once amonth when I start it up to charge the battery and circulate the oil it has been sitting for about 3 or 4 months. I tried to drive it last week, but when I got in the brake peddle went right to the floor. I pumped them for a while with no luck. There were no fluids on the ground and the master cylinder was full. There were no warning lights on, and I didn't have time to mess with it. A week later the peddle went to the metal again, but this time the brake warning signal was on. The last time I drove it, 3-4 months ago, the brakes worked fine.

ABS ? Bleed your brakes? This sounds like you need to rebuild your master cylinder. Easy to do. Clean out your resevoir while your at it. Make sure that the small holes at the top of the master cylinder or clear, if your brake fluid is not clear change it! You will be surprised at the amount of crud that is at the bottom of a brake fluid resevoir.