Computer randomly restarting

Question

I just got a new graphics card a gtx 1650 super, so we put in there it worked fine. the next morning however it crashed whenever anything opened. then one time I was able to open a fairly demanding game and play it for a bit then I quit the game and then it crashed my computer. my dad then thought it was a power supply issue so we threw a better power supply in there and that fixed it for the day. now, this morning when I started my computer and opened steam it crashed instantly now whenever I have something more demanding than google open my computer screen goes black and restarts itself completely. I was able to play a very demanding game this morning and thought the issue fixed itself but I opened discord so I could play the game with my friends then it crashed almost instantly. I have no idea what the problem is sometimes I think discord crashed it sometimes it seems nothing at all crashes it. please help I am very frustrated