IMac not recognizing correct Administrator password to use Time Machine

Any suggestions on how to get my Mac to recognize the correct Administrator password would be much appreciated. Mac I7 27" late 2009 OS Yosemite 10.10.5.
We were trying to get a old external hard drive (A network drive GoFlex Home) to work but was unsuccessful - maybe it need a new cable.
Then when I rebooted, non of my internal hard drive mounted, reboot a few more times, the internal hd showed up, again and again, the ssd boot drive shows up. The computer seems to be working fine, but I cannot make any changes as my system preference is locked - not recognizing password.

Since the computer will not recognize the correct Administrator password – I cannot use Time Machine to go back to where I once was happy and working. Any help would be much appreciated.

I believe your problem is the drive you are trying to use. Big problems GoFlex Home:-


https://discussions.apple.com/thread/3231868?start=30

I think agree with you harryb2448. After spending 5 hours starting and and restarting, changing boot drive, open in safe mode, etc. As I was about to change my Admin password (with much trepidation as I know I do not know enough to mess with Terminal). I reboot with command r, the dialogue box came up to select the boot drive. Though I'd give it one more try, and selected my original boot ssd. Voila, everything was as it was, recognized my original Admin password and the world is whole again! I don't know what happened, but not looking a gift horse in the mouth, I'll settle for working. Thanks for your reply and I'm going to throw this GoFlex drive AWAY!

Good work I hate Seagate stuff. Used to be tops too!