my immediate vendor is not paying or responding

My Situations where my immediate vendor is not paying or responding my calls.

A : Main vendor (Paid money to B as sub contractor)

B : Sub Vendor (Not responding to any calls, not paying money to company C)

C : My company has not paid for 3 /4 months from B (Corp-to-corp)

Company B is based out of MI. They are not responding.

As per Contract, Company B should release payment with in 5 business day. Also contract with B, shows i (My company C) shouldn't join Company A anytime or have direct relationship with A.

I have sent several emails, FAX & voice messages. NO response. Since Company B is not following it's own payment contract , can this contract be Invalid or does this gets invalidated?

Let me know, how to approach this?

I am negotiating with Main vendor - A , to come with a direct contract with me /my company C.

Company A is giving below suggestions :

There is one possible solution.If you are ready to indemnify Company A. and our client from any liability arising out of Company A. entering into a contract with you / your company C directly,we may be in a position to consider this option.Please understand that such a commitment will be legally binding and formally documented and executed by you.

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What are the options / negative side of this new contract with company A?

What are the precautions to be taken while signing this new contract ?

Is there any legal problem going forward if i go with company A?

Thanks for your advice..