Everytime I open java and hit play, it loads half way, and stops responding.

Last night, my brother got on to play. i had already opened minecraft in the latest release, 1.16.4, but he wanted to play on the combat update (1.8.something), so he re-launched minecraft in that update. however, it would not launch. we tried re-launching it again, but it said that it was already running (which it obviously wasnt). we tried to launch it anyway, but it just wouldnt launch at all. we played diferent games instead then turned off the laptop hoping it would work tomorrow. when i got on, just now, i tried minecraft, but again, it was already running. i tried to start anyway but all my laptop did was get laggy. i opened task manager to see why it was laggy, and found that the java binary thingy was taking up 70% of the CPU. it was in backround programs, and i am still wondering why. then, i tried again, and minecraft finally opened. i was relieved, until i realized that it wasnt doing anything, with the loading bar only half way. then, i tried to open the windows start, and then a window popped up saying "java(something) binary has stopped responding". i waited for it to respond, but it just didnt. i stopped the program, went into control panel, then repaired the launcher. i felt that the binary was the thing that launched it, so i thought repairing it will replace the binary. it did not. how do i fix this?