Hmmm...
Ok, before you go changing a bunch of stuff around, let's backup a little and try one more test. I feel if we have you manipulate RAM, battery, gpu, etc. all at once we are adding too many potentials too early into the troubleshooting. I like a one rabbit hole at a time approach.
Gotimo, you mentioned that everything seems to be working just without visuals...Are all fans coming on? [The gpu fans may not for they may have a setting for only coming on under load or at certain temperature thresholds] You said no beeps, so maybe it is posting just fine, just not to the screen. So, I recommend we try another simple test. Make sure you are powered off and unplugged from the wall. Plug your monitor into the motherboard I/O at the rear of your computer and remove your dedicated graphics card physically from the motherboard and unplug its power connection to the power supply...basically, completely remove it from your computer. This will force your computer to use only the integrated graphics in your cpu and motherboard. Power the system back on and let us know if you get anything on the monitor.
My theory is that there may be a driver or gpu issue (it could be BIOS as well, but isolating tests are important, so we won't try that yet) and by removing the dedicated gpu we might get visuals that will allow us to test and solve on a software level as well as a hardware level. Also, please list your full specs so we can know exactly what parts we are working with...this could help us root out any hardware conflicts and allow us to research your parts to try to understand if there is a common issue at play between any of your components.
So, let us start with the simple test above and then we can go from there depending on the results.
p.s. I removed the 'solution' accredited to me above for we haven't solved your problem yet...🙂