Optiplex 760 startup faliure

The 3rd LED is usually a CPU error. Try unplugging everything from the MB except for the power connectors and try to boot. If it boots then one of the components such as a hard drive is bad. At that point plug in the components one at a time and try booting after plugging in each one. If it boots fine until you plug in a specific component then you have found the problem. If the system does not boot then you quite possibly have an MB or CPU problem. Keep in mind that the 760 is around 12 years old now and you may be looking at upgrading to a new and much faster system.

Re: It only blinks the pwr button

if no post and power button blinks amber, first thing to try is replace CMOs battery with new one and clear CMOs settings by reset CMOs jumper on motherboard.  Is this 760 MT, DT, or SFF?

Its 2 am but i try both suggestions. Thank both of you.

Its a sff and i replaced the battery. I forgot to do the bios reset(duh) but thanks the reminder.

Sadly i dont have the money to buy a new one. And it was my leader teachers pc that died a day before her, so my goal is to repair it and use it as a memory

Tried your sulution. Fail now both 1, 3 and pwr button led are blinking( still amber pwr button)

next test to try is to replace the 760 sff psu.  this model uses mini 24 atx.  it is compatible with 780 sff psu.