Second partition does not boot.

Mac OS X v10.6.8. At purchase 5 years ago, I partitioned 1 TB 50/50, and set up the second partition so it never connects to Internet.

Method to boot to HD2: Press Option when turning on Mac. Slot and padlock appear. Type password and hit Enter. HD and HD2 discs appear. Select HD2.

Hit Enter. Boots to the two accounts on HD2. When these appear, Internet connection turns off. Choose an account, Enter.

Processor speed. 3.2 GHz, Memory 4GB.

This has worked perfectly for five years. Now, Select HD2 and Enter, but HD2 accounts do not appear. The blue screen appears and stays.

Mac will not turn off from this condition. It is necessary to turn off the power switch. I repaired the permissions and repaired the HD2 disc, but no change.

I have everything backed up in Time Machine, Acer 1 TB external disc. I have not changed anything on the computer.

Can anyone help? Thanks.