I recently purchased a Lenovo S20 ThinkTank, a refurbished computer from 2009 (not used very much according to the refurbisher). I have had some minor RAM and software issues with it but I do not believe it is related to this.
I also bought a Radeon RX 550 for the PC. It was first installed when the card was very new, so the drivers it was running were from the initial release. Close to three months later I started experiencing video output stopping - it would claim it incompatible resolution with monitor, incompatible refresh rate, etc. which is incorrect. I checked the GPU temp, fan speeds etc and everything seemed in order despite the output issues.
I then updated the drivers to 17.5.2. Then it would not boot past the windows screen at all before video output stopped completely (monitor light yellow etc). So, I went into safe mode, carefully uninstalled 17.5.2, and rolled back to the default drivers, but the same issue is now persisting. I'm not getting a boot at all.
Let me know if you would like a dxdiag or more complex specs.