Motherboard battery change.

[buffykibby]

My partner changed the battery in his optiplex 755 and now all we get is a black screen. Checked all the cables and made sure everything is where it should be and nothing not even a beep. Not even a message no signal in. Any help would be greatly appreciated.

 

[zoltan.boese]

I am sad to hear that. Does anything light on on the motherboard? Does the motherboard do its power on self test (POST)?
Have you read these guides:
http://www.tomshardware.co.uk/forum/261145-31-perform-steps-posting-post-boot-video-problems
http://www.tomshardware.co.uk/faq/id-1893016/post-system-boot-video-output-troubleshooting-checklist.html

 

[zyh1987]

did you flick back the power supply switch from O to I?