menu and slider don't show at all browsers

The first step towards browser compatibility is validation.

I read the Validation report could you guide me how to fix it? I am not a tech person. what might be causing so much problems (actually I might even understand the problems just by reading the report to be honest)

Here are explanations of all errors generated by the W3C validator.
Solve the first error (at the top of the list).

I got this error
error message [25]: “general entity X not defined and no default entity”.
What does this mean and what can I do about ?

also I can’t find in anywhere pinboard’s basic information on browser compatibility, what codes is it built on. I am wondering my issues can possibly be incompatible with some versions of browsers?

Try querying this on their dedicated support forums.

THanks Andrew for helping. I kind of gave up on the theme now:(