Blinking RX led on Arudino

At the first for few tens of minutes Arduino runs normally, but after that the RX led on Arduino start blink and I cant upload code, do any of you know how to fix it, even when I do not exactly know what it is? I have seminary tomorrow and I need that Arduino and if it will not work I will not pass.

Disconnect everything you have connected to it , try and upload blink , if that’s no good , press reset as it’s about to upload after compiling.