Re:  grab a small video card and try? Only if you already have one.  Test with what you have around.  Depends on what type of monitor inputs you have, try different cables, adapters.  I use Dell adapter, but a basic adapter would work as well. If you are connecting to a 4K TV using HDMI cable, check your TV settings to see if you can change HDMI to enhanced mode and try both HDMI2 or HDMI3.
Hi all: longtime reader/first time poster.  I have a Dell Optiplex 5040 SFF with a SSD drive running windows 10 Pro.  It's on HDMI to a TV that doesn't show me anything for the first 30 seconds as it tries to find the "type" of device"  After owning it for 7 days, I plugged it into a DP monitor to go into the bios so I could boot from USB.  Here's what happened a) I noticed it says "Invalid Format" in yellow text then boots to windows, no problem even to hit F2 to go into Bios b) I restarted and tried f2 but then it sticks on invalid format and won't boot to windows nor will it go into the bios. c) booting from USB isn't recognized. d) so I opened it up and changed the sata cables out, thinking then I could get to the bios: nope just invalid format. Any options or Ideas would be appreciated. Sadly the reselling company (allegedly a Windows Refurbished) responded saying that since I opened it up my warranty is void. 
Invalid Format on boot, can't go to bios