Admin login page is loading very slowly . Some times it does not load at all.

“Request Timeout
This request takes too long to process, it is timed out by the server. If it should not be timed out, please contact administrator of this web site to increase 'Connection Timeout'.“

After changing php version (to any other version number and/or changing memory) it loads fine until login in again a few hours later. Server techs said they checked the server and can not fault the settings. They also have increased the connection timeout.

I am just curious if during upgrade from 1.5.3 to 1.5.5a some of the files did not updated correctly. I do not want to re install or upload all the files again as the site is working fine.

So which files should I pay attention /re upload to fix this problem?

I have also read that turning of version check might increase load time. I did that in admin but still version check at the top right hand corner is showing. Is this an indication that some admin files did not upload correctly? if so which ones should re upload?