At 0834 EST, the pilot departed Bradford Airport on an IFR flight to Alton, IL. About 4 minutes later, he advised that he was having difficulty with his flight instruments while in IFR conditions. He attempted to return to the departure airport by using D.F. steers, but was unable. He then contacted Cleveland Center and was cleared to climb to 8000 ft MSL. The center recommended that the pilot proceed to Toronto, Canada to the nearest airport with acceptable weather. However, the pilot was unable to control his altitude and heading, and subsequently, entered a dive and crashed. The HSI (attitude indicator), directional gyro and turn coordinator were found to be pneumatic pressure instruments, all operating from the same system. The pneumatic pressure system incorporated two pressure pumps, one on each engine. An inspection of the pumps revealed that both pump drives were sheared. Radio calls from the pilot had identified that all pressure instrument readings were faulty. Weather: turbulence, low ceiling, snow.