help...plz...Urgent

Hi.
I came to qatar with work visa ( visa was under my name) under a company.but
it is felt theat company is not good.
my visa is not stamped on my passport and didnt apply for RP.
I applied for qatar vacancies and i was called for an
interview by one company next week..

my question is ?
1, will it be possible for me to shift to another company.
2, Is it required NOC from the sponser.
3) How should i proceed with visa process?.
4) If the new company redy to give new visa for me,what is the procedure?

I need genuin answer from you all dear.