hardware raid 5 and software raid 0 stripe broke.

We have a Linux box running redhat 7.2   We have two hardware 
controllers in it with about 500gig's each.   They're raid 5.   We were 
using a software raid to combine them all together.   1 hard drive went 
down so we replaced it and now the system won't boot.   We have used a 
Knoppix boot cd to get into a linux system.   We can see /dev/sda1 and 
/dev/sdb1.   However, /dev/md0 cannot be accessed.   Is there a safe way 
to create the software raid from the cd to see if maybe mdadm on the 
original system got corrupt?   any help would be greatly appreciated.

Sincerly,
Ken