Vtiger Fix

Description of support work: I have a vtiger CRM installation on my bluehost site hosted. It worded fine for few years until it stopped working in last few days. I am still able to log into the system but when i click on any of the modules (instead calender) it gives me HTTP 500 error.

I need someone to be able to fix this. It is definately a small work and i am suspecting it to be php issue but i can't figure it out myself.
Extra notes: The CRM site has lot of data so while fixing it my data should not be lost.

Please send me your proposal to fix this. I will give you accesss as required.

Thanks