A solid white LED was a good sign, indicating your system is alive and repairable.  Previously described symptoms indicated some type of hardware failure.  Since the system was not in use for a long period of time, system CMOS backup battery needs to be replaced with a fresh new one, and you did.  Although not mentioned, you must set system date and time, then adjusting BIOS settings to match with your installed hardware. With a progress, you gained the system display and was able to access BIOS menu.  The next process is running diagnostic scan to identify any hardware failure such as memory, storage drive, etc.  To access one time boot menu, use F12 key as similar way of F2 for system BIOS setup. If any issue is identified, it needs to be correct and resolved.  Some issue may not be picked up by a diagnostic and have to be inspected manually.  Hence the request for system hardware setup, which making it easier to spot issue or error and resolving it. At that point, you should be able to perform a fresh installation of the operating system as it's a sure way to get your system up to date with a least amount of time spent.   I outlined these steps so you can proceed without having to wait and come back with next question.  
So this happened about a year ago and what would happen is when I press the monitor button, I will show amber for 1 second then just solid white with no blinking. The monitor wouldn't turn on and the case felt cold where as before it would warm up a little After that I could hear the fans moving really loud and when I open the case it looks like they are at max speed.  A year ago when I checked it was really loud now the fans are more quieter as I have to put my head near the case to hear it well. On the back there is the light beside the Power cable that still turns on. A few days before all this I noticed every time I tried opening a game, my entire screen would freeze and I would have to sign out for it to work again. Sometimes it wouldn't freeze but windows would say it stopped working. However when I opened browsers or any other program it works perfectly fine. That is all I know right now does anyone know what the problem could be?
Optiplex 9020 Solid white monitor button, monitor won't turn on