msi b450 carbon

Hello, I have bought a new case for my PC and have installed the motherboard along with all my original components. The PC worked without any issues previously. After installing all of the components in the new case I attempted to boot the pc however a red light near the IO shield blinks 3 times...

Atm I'm going to buy a r7 2700, but I am wandering if I should wait and buy a r7 3700 because the 3700x is supposed (don't know for sure) to hit th 5ghz mark with 12 cores, since the 2700 is £200 rn witch is a pretty good deal, I'm gonna be doing alot of gaming and video editing and...