Hydraulic Brake Prob.

What brakes are they and how old is the bike?- if they use DOT fluid such as Avid, the fluid volume may have increased as the fluid has absorbed moisture from the air. Are the levers really hard with no free-stroke? You can try letting a tiny bit of fluid out of the system to allow everything to move again but be careful not to let air in and make sure you wash down the area afterwards with water as the fluid will strip the paint off if left there. You should only need to crack the bleed port at the lever just open. The excess fluid will come out then you can tighten it back up and test for drag.