Try the password jumper. Details in your online Optiplex 745 manual.
I have forgot my BIOS Administrator Password,and i cannot perform any changes! I have already tried removing the CMOS battery,but it didn't work out.Is there any way i can unlock my BIOS? I want to change some settings so as to install new hardware,but i can't! My computer is Dell Optiplex 745
Locked BIOS