sing\sang\___

[Mariner]

Actually, you can use "I sung a song yesterday". According to Leech & Svartvik, the past form allows both "sang" and "sung". However, it is rarely used. (British national corpus returned 96 hits for "he sang" and 2 for "he sung")

[florr0]

Originally Posted by j_carhaenni

I sing a song yesterday.I sung it very well. everybody is happy to hear that song i sung.

You're using two times the Past Participle form of "sing" without a form of "have", wich is quite impossible.

[philadelphia]

SIng sAng sUng a song