Having Server Error!! Please Help

[ArmudShop]

This my first post here in the forum and I need help.
I used prestabox to make my website domain and then tried to upload a theme with no any success.
Then when I made a host with hostgator and then didn't know where to paste the servers numbers that I get it from it.. maybe I put them in the wronge place in prestabox and now having this:

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, [email protected] and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

I 've sent emails but with no reply till now, Can any body help me to fix it?!
Another thing, I tried alot to open my website with filezilla but it didn't open there.
what do you think is the problem?!

waiting for your kind reply..
Best Regards,

Maya