[svandamme]

You have mirrored disks.. so they both have full copies of all data.

That it locks up , could be a problem with the data (software) , or with the hardware (disks, motherboards, sata controller)


Start by disconnecting everything you don't need.
Disconnect ALL usb stuff you have on that pc
If you have add on cards, get em out
Disconnect the CD rom


If it still doesn't boot now..

Disconnect both disks, see if it gives you a different error like "no boot disk, retry"

If that works, add one disk
If that doesn't work
remove that disk again , try the other one.

still nothing? try those disks in a different pc.