Cannot access enable mode(privileged) at PIX 535 ???

Dear ,
Yesterday, there was electricity down for about three hours. I turned off PIX 535 appliances (Active/Standby) by set  switch in the back to 0. I turned primary unit first , and after that turned off secondary one.
Today, I cannot access enable mode(privileged) ???
I can telnet PIX , then login (put my user name and my password) , so I can reach unprivileged mode (PIX>).
After that I trying enter privileged mode (PIX> ena ), password prompt appears, I put the password, but unfortunately not accepted.
Currently, I can access firewall by ASDM 5.2 , I tried to change enable password from :
[ Configuration --- Properties --- User Accounts --- enable_15] but not success.
Also I tried some estimated password (cisco,pix,ciscopix,password,enter without) but not success.
Dear Expert, could you assist me to access privileged mode through Telnet ?

Thanks in advance ,,,