Need help with brakes...very sensitive?

i have a 1992 chevy s10, 2wd, abs, 5spd manual, 2.8L v6. it's been sitting for awhile, but i've been starting the engine at least once a week. today i took it out for a short drive, and when i just tap the brake pedal it suddenly stops short and skids. they are very sensitive. what could this be. never did this before.