My HP Pavilion Desktop 510-a010 problems

Let me preface this by saying I’m a teen in high school, so please don’t hate me if I’m missing an obvious sign. Ok so I got this PC from my grandma. I’ve always wanted one to play games on, so I obviously accepted anything cause it’s my first ever pc. It’s a HP Pavilion Desktop 510-a010. It worked just fine at her house, but when I plug it in at mine along with the monitor it came with, it took forever to load. I’m talking multiple hours. After it finally turned on, all I could do was move my mouse around while it beeped every time I moved it. I couldn’t click anything because it wouldn’t register or do anything. This was about 6 months ago. It’s been sitting on my desk for a while and I decided to try again. This time the sound is off and the mouse moves kinda smoother but still can’t click anything. I need help! I got a yellow cord with it that I assume plugs into a router, but that’s not in my room and I thought it wasn’t vital but maybe it is IDK! I would appreciate some advice!