spurious voltages on the hdmi cable and induced voltages can cause something like a capacitance to build and cause issues...
Turn off PC, unplug monitor hdmi at both monitor and pc, UNPLUG THE PC. Let the power supply drain (wait a few minutes). Unplug the monitor power.
Now, connect monitor and pc hdmi. Plug in monitor and plug in pc.. if all goes well the spurious voltage that was there will disappear.
If it comes back - check you are not running power cables un-shielded next to your monitor cables or other cables going to or from pc. Just give them some room... cheap cables are highly susceptible to cross em interference.
Try using another, better quality preferable, hdmi cable also. Make sure there's no dust on the pins or components. If you have access into the PC - carefully follow manufacturer recommended cleaning (gently air dusting to remove dirt building up on main boards and graphics cards or other components - especially in the power supply and graphics connection points. DO THIS WHILE IT IS UNPLUGGED!!!! If you don't know what you're doing - call a friend that does.
If all else fails - check your power supply voltages and make sure they are all within normal tolerances. Some monitors are easily damaged by unbalanced grounds on the hdmi and main power. There may be dangerous reverse potential on the neutral or ground lines as a result of a failed diode or something.. can't tell you all the many ways I have seen electronics lose their magic smoke but there are many possible physical component issues possible.
By far the most likely is that the cable is bad or there is some random spurious voltage that has been induced on the line somewhere. HDMI has power on it and if there is a connection that is not solid or any standing waives from a kink in the line or otherwise it can cause issues... just replace and be sure to keep the ends clean and dirt free. Things happen even when they are not moved or touched.. try to troubleshoot and good luck!
Of course - if the signal is weak and you're running too far it can cause issues too.. again - a better cable with lower impedance can help there too. Always check sync freq and normal driver updates too. That's a no-brainer... keep your drivers up to date. There's usually a reason a manufacturer releases a driver update when they take the time to do so. I use a couple tools from IOBIT to keep my family pc's up to date and running smooth. Love the one-click button options - super easy to use - Advanced System Care Pro. There is a free option too - but the pro is pretty cheap and well worth it - and can be installed on several PC's if I am not mistaken...
Let us know how it works out!