I was trying to go to sleep last night, but I couldn't because someone was playing a musical instrument next door.
I was ready to go to bed last night, but my neighbour was playing an instrument too loud and it kept me awake.
ーI was trying to go to sleep last night, but I couldn't because someone was playing a musical instrument in the apartment next door.
「昨夜寝ようとしたら、アパートの隣の部屋で楽器を弾いていて寝れなかった。」
play a musical instrument で「楽器を弾く」
in the apartment next door で「アパート・マンションの隣の部屋」
ーI was ready to go to bed last night, but my neighbour was playing an instrument too loud and it kept me awake.
「昨夜寝ようとしたら隣の人が楽器を弾いていてうるさくて眠れなかった。」
it kept me awake で「それは私を眠らせなかった」となり it は楽器の音を指しているので、楽器の音で眠れない、という意味になります。
ご参考まで！
I was trying to go to sleep last night but I couldn't because my neighbor next door was playing an instrument.
ご質問ありがとうございます。
・「I was trying to go to sleep last night but I couldn't because my neighbor next door was playing an instrument.」
（意味)寝ようとしたら隣の家が楽器を弾いて寝れなかった。
<例文>I was trying to go to sleep last night but I couldn't because my neighbor next door was playing an instrument. I'm so sleepy and tired.
<訳>寝ようとしたら隣の家が楽器を弾いて寝れなかった。とても眠くて疲れています。
ご参考になれば幸いです。
カナダ 
アメリカ合衆国 
