Need advice very badly in employment contract and employment pass

Hi guys,
Lets go straight to the point.
I got an offer from a A company and i have already signed on the employment contract, they are also processing my employment application.
But now the problem is A company is dragging me too long. I been waiting from November 2012 till now. I just received the IPA letter from them but i am still waiting the body checkup to be done.
I would like to give up the A job now as i get a very good offer from B company.
So now my problem is will there be any problem if i back up from my A job now? Especially for the MOM side as my employment pass was rejected before and finally get it through appeal.

Besides that, there is also a condition in the A company employment contract which is "Termination of employment before completing the full training = Liqidated Damages Amount to be Paid :SGD 30000".
So i would also like to know that will this condition counts anot?
FYI: Currently my situation is A company: Received IPA Letter, Waiting for Arrangement on body checkup, Signed on the contract
B company:Just received letter offer

Please don't hesitate to ask me for any more information, as i really need advice very badly.
I really like the second job which is from B company

bump please

So you have a valid (signed) employment contract with company A and it specifies a penalty if you terminate before commencement. And now you want to terminate it before commencement? I think the case is very clear: You need to pay the penalty, as you have agreed to by signing the contract.
Company A must cancel the (already IPA'ed) EP before company B can apply for a new one. The new one can be rejected by MoM. This is the risk you take, and you might end with no job and no visa (which means you'll have to leave Singapore).