I think you have unplugged the speakers while inserting the RAM. Since we can't see your open laptop, check out it by yourself whether speakers are connected or not. Also try once by downgrading the RAM to original/previous state. There are very fragile wire connection - it could be that it's got broken.
This is Juniper, a web developer who loves to work on Dell machines only. My hobbies are teaching, reading idioms and old sayings.