目覚し時計が鳴らなかったので寝過ごしてしまった。

I overslept because my alarm didn't go off.

目覚(めざま)し時計(とけい)が鳴(な)らなかったので寝過(ねす)ごしてしまった。

Mezamashi tokei ga naranakatta node nesugoshiteshimatta.

目覚ましい (めざましい)

brilliant; splendid; striking; remarkable

時計 (とけい、ときはかり)

watch; clock; timepiece

が (が)

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

鳴る (なる)

to sound; to ring; to resound; to echo; to roar; to rumble

ので (ので、んで)

that being the case; because of ...; the reason is ....; given that...

寝過ごす (ねすごす)

to oversleep

Readings: モク、ボク、め、 -め、ま-

Meanings: eye, class, look, insight, experience, care, favor

Readings: カク、おぼ.える、さ.ます、さ.める、さと.る

Meanings: memorize, learn, remember, awake, sober up

Readings: ジ、とき、 -どき

Meanings: time, hour

Readings: ケイ、はか.る、はか.らう

Meanings: plot, plan, scheme, measure

Readings: メイ、な.く、な.る、な.らす

Meanings: chirp, cry, bark, sound, ring, echo, honk

Readings: シン、ね.る、ね.かす、い.ぬ、みたまや、や.める

Meanings: lie down, sleep, rest, bed, remain unsold

Readings: カ、す.ぎる、 -す.ぎる、 -す.ぎ、す.ごす、あやま.つ、あやま.ち、よ.ぎる

Meanings: overdo, exceed, go beyond, error