I am having PIX515UR bundle and single pIX 515. This two pIX are for two different networks of customer. The PIX 515FO-bundle is configured in failover mode. while  another PIX - 515 is running as a standalone. 
The single 515 has failed , and till the time i get it replaced , i want to use one of the PIX from failover bundle.
I tried it to use , but its not comming up.
I used command no failover and tried to make it active.
it worked fine , but after 24 hours it got reset once again..........
is it possible to use PIX in failover bundle as to different PIX ?????