[support] Admin pages not working - login makes site "freeze"

[Peter Metelerkamp]

I have a few Drupal sites on a shared hosting account. They are all 
using 6.10. Each is in its own directory under public_html, with its own 
installation (i.e. not multi-site). One of the sites, at 
www.settlercountry.org <http://www.settlercountry.org>, which has been 
working fine for a few months, and another site under construction, have 
the same problem:

This is that the site works fine for a viewer, except that the search 
function is not working. But when I login as admin, the site "freezes" - 
i.e. the links do not function and I am unable to navigate to any part 
of the site, admin or frontend. I cannot logout unless I clear cookies 
on my local machine.

The error log in the Cpanel of my account gives "File does not exist" 
messages, but the path is what you would expect it to be.

The other sites under construction on the same server and hosting 
account (but not yet active with content), are working fine; one of 
these is very much more complex and uses dozens of modules not used by 
the "problem" site which is pretty basic, as you can see if you go to it.

I have not touched the databases.

I would be very grateful for any advice! Please make it simple to 
understand, as I as far from expert as it is possible to be, and am 
fairly new to this outstanding system! Thanks very much in advance.