A CRJ200'S RADIO ALT FAILED AT FL250. ACTIVATING ALL GPWS AURAL WARNINGS. AN ALT OVERSHOOT OCCURRED DURING TROUBLESHOOTING AND RETURN TO LAND.

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LEAVING ZZZ FOR ZZZ1 CLBING THROUGH FL250 WE EXPERIENCED A RADAR ALT FAILURE INDICATING '0' FT AGL. THIS CAUSED THE GPWS TO START WARNING 'TERRAIN; TERRAIN; PULL UP' CUES AND OVER AGAIN. I WAS THE PF WITH THE AUTOPLT ON. THE CIRCUIT BREAKER TO PULL IS BEHIND MY SEAT. WITH THE GPWS WARNINGS; COM WITH THE FO WAS UNCLR. I TOLD CTR THAT WE NEEDED TO RETURN TO ZZZ. HE GAVE US A STOP CLB AT FL260. WE WERE CLRED TO FL280. OUT OF FL250 I SPUN THE ALT ALERTER TO FL260. WE STARTED GETTING OTHER FAILURES THAT ARE ASSOCIATED WITH THE RADAR ALT: TOO LOW GEAR; TOO LOW FLAPS; SPOILER FAIL; LIGHTS AND CAUTION MESSAGES. I PULLED CIRCUIT BREAKER RAD #1 TO STOP ALL THE AURAL WARNINGS WHEN I NOTICED WE WERE AT FL275 AND CLBING. THE AUTOPLT DID NOT STOP AT FL260. I STARTED BACK DOWN TO FL260 WHEN ATC CALLED ASKING WHAT WAS WRONG. THEY KNEW WE HAD PROBS AND WERE CONCERNED ABOUT OUR ALT. THEY THEN CLRED US TO FL240. FACTORS: GPWS NOISE; CAUTION LIGHTS; ASSOCIATED FAILURES WERE DISTRACTING. CIRCUIT BREAKERS BEING BEHIND MY SEAT DIVERTED MY ATTN. FO WAS BRAND NEW LESS THAN 100 HRS IN TYPE AND 500 HRS TOTAL TIME. AURAL WARNINGS WERE DIFFICULT TO TALK OVER AND FO DID NOT SPEAK ENGLISH AS HIS PRIMARY LANGUAGE. TCAS; WINDSHEAR FAILURES; FLT SPOILERS; GEAR WARNING; DECISION HT; FAILED WITH AN INST APCH INTO ALT WITH INCREASED LNDG DISTANCES WERE ALL ON MY MIND DURING THE MALFUNCTION.