Applying H4 visa with stamped H1B

I have H1B visa stamped.Valid till May 2016. My husband is working in US. As I do not have projects in my spouse location,my husband planned to take me by applying h4 dependent visa. My questions are,

1.Will my H1B cancelled when H4 is approved?

2.If I get H4 with H1B cancelled, can I try job in US by changing my H4 to H1B as my petition is approved till May 2016?

Please advice.