|Oh, it's just the monitor logo and not the video adapter. Often a video adapter such as Nvidia will identity itself prior to the normal PC logo or posting screen. It's often missed because it would be the first thing that shows on the screen and then only for a moment. But with yours nothing ever posts from the computer itself.|
Did anything happen to the computer or did you make any changes to it between the last time it worked OK and the first time it didn't?
I know this doesn't narrow it down but it could be the power supply or motherboard. Fans and drives spinning up and LEDs flashing only mean the PSU is providing 5 and 12 volts. The motherboard itself needs other voltages at sufficient current. If you have a working compatible power supply you may want to swap it in and see if it works then.
Or often motherboard manufacturers use low quality capacitors that eventually go bad. If so it'll often be those surrounding the cpu. They'll get a puffy look like a soda can that's been in the freezer too long and maybe some dried residue on the top indicating leakage.