I opened up my computer to clean the fan and now monitor is black

[Kimscare]

I opened up my computer to clean the fan and now the monitor won't work.

 

[vesp3r]

Do you hear the computer starting or its only the fans spinning?
If you hear the windows sound and still dont get signal on monitor check if you have your gpu connected properly. Also what exactly did you do while cleaning: Blowed dust with compressed air only or you deattached parts and used other stuff to clean?