Pc has weird posting issues

[Cuboid88]

Hey, I recently turned on my pc which hasn't been on in a month and it's giving me a weird posting error. Basically, I turn it on all the lights turn on as should, I get the satisfying beep from the motherboard. My keyboard light turns on but my mouse doesn't and I get a black screen on my monitor. I checked to see my monitor was still working I hooked it up to my MacBook and it worked fine, I've also fully switched it off disconnecting power and everything and turned it back on again but still nothing. I find it weird how my keyboard lights up but my mouse doesn't and that it was working fine a couple of weeks ago 

 

any help is appreciated