This is a bit of a techy one, but its got me stumped.
When I try and visit the homepage of my website, I get a download dialog saying "you have chosen to open www.mysite.co.uk which is a application/x-hhtpd-php53 file".
Oddly, all other pages work fine. I have looked at the htaccess and there is nothing unusual. Another quirk is that if you visit www.mysite.co.uk?flush=all, it loads fine. If you then go back to the homepage (I supposse the new cached version) you get the download again.
I have tried disabling the cache in the config file, but this doesn't help.
That looks like a server misconfiguration. Have a look for that string in the server config or the .htaccess and replace hhtpd with httpd. If you don't control the server config then maybe add something along these lines to your .htaccess file.