If your newly bought graphics card did not work, try to return it.  If you planned to upgrade your Optiplex as a media machine for your TV, get a better graphics card capable of 4K playback. You would have better chance of resolve the issue on your own rather than waiting for some one else.  Just use integrated graphics connection for now and try F12 at every boot hoping that your TV set will adjusting proper resolution with EDID signal. 
Hello!   I tried a setting in BIOS because my PC didn't recognize the video card, what I bought. I turned OFF Legacy Option ROMs, and I turned ON the Secure Boot. The system is/was on UEFI mode. Since then I can't open the BIOS, and the Dell logo doesn't appear after turning ON the PC. Before these settings, I had no problem opening the BIOS. My PC connected to a TV with a HDMI cable. When I try to open the BIOS, appear a message on my TV screen: Not supported resolution. Change the resolution of the external device. Interesting is the Windows is boot perfectly, only the BIOS and the Dell logo not appear on the screen. I removed the CMOS battery, waited for 30 minutes, and I put back the battery, but the problem doesn't solved. I have not a monitor, so I can't try it other screen. How can I solve the problem? 
Bios menu not appear on screen