1. Could be the ebrake switch, you would have to take off the cover to see this, could be stuck down

2. Check to see if you have either a leaky wheel cylinder, caliber or brakeline.
Check to see if the brake switch on your brake pedal is bad. Also check to see if the master cylinder is leaking into the the brake booster

3. If those are OK, then your proportional valve most likely has to be replaced, and then bleed the brakes with the key on but not running