By removing and re-installing the battery, you have effectively done a BIOS clearing. Usually that means that, IF your mobo has a video output system built in, the BIOS will default to using that. So IF you have that AND you were using your own add-on video card before (with the BIOS set to use that card), you just re-set the BIOS to ignore that card! In that case, connect your monitor to the video output port of your mobo and you should see a display that way. Then you can re-adjust the BIOS the way you want and re-connect your monitor to the video card instead.
By the way, when the BIOS is re-set this way, sometimes it does not get exactly the right default settings for other things, too. Of course, to do any adjusting there you need some basic video output to see. But if you get that, go into BIOS and look (usually near the last menu tab) for a place to restore some selected set of default parameters. The best choice usually is Optimized Default or something like that. Do that restore, then Save and Exit, and go back into BIOS again to adjust your video output settings, then Save and Exit from there.