Did you try restarting the server?
Do you have a PHP accelerator installed (e.g. eAccelerator, APC, XCache, WinCache, etc...)?
Luis, thanks for the feedback.
How do I check if this is installed?
How do I restart our server?
> How do I check if this is installed?
The easiest way would be to check the output of the PHPInfo() command. There's a section in the output of PHPInfo() that tells you which PHP accelerator is installed, if any.
> How do I restart our server?
Push the power button!
Seriously, it depends on your OS. In Windows click Start / Shutdown / Restart.
Unix? I'm not sure... perhaps: shutdown -r
Or just bribe your IT guy to do it.