Main domain dropped , while subpages are ok...

Hi everyone .
So as the title says my site dropped on google searches.
The main domain can not be found in any google search , only if i type it's name .
It used to be on the first page for 3 most important keywords for one and a half years.
One month ago when it happened i said it will get back...it's only google playing.
So nothing ...it dissappeared for good, the subpages are cool, on the second pages for searches.
I did found out after i started reacting that my hosting company changed the server , including the IP address. They say all the required steps were followed so nothing would go wrong.( kept the old ip for a while...redirected..and so on )

Now ...i have no ideea who's fault it is . I am upset though , they could have send me an e-mail saying that they are doing changes on the servers/site...

I went in my webmaster google account and i think all is ok ...the same.
I did not messed with it before it dropped, no major changes..
Same meta tags....same pages...

I did notest something weired ...i have a subdomain for different keywords . In webmaster Tools (for the main domain) i've seen that the G-bot sees keywords from the subdomain too. Strange indeed.....

I have no ideea what is wrong...I searched the net and found some posts but nothing gave me a solving ideea.

This site gives me the clients i need to keep working...very important.

Thanks so much to those willing to help me.