I checked my mainfile.php. Everything is fine. Has not been overwritten but yet I get a blank page when going to http..../upgrade/index.php

Help. I have uploaded all the files cannot run upgrade script.
Actually had this problem when trying to install a module today. Just got a blank page after the attempt. Refresh brought back the module page but the module never completed an install.

So, I thought I'd do an upgrade to fix my bug. Now I am stuck. Really need good advice, quickly.

Everything is white. Lost the whole site. This is a major problem. I need expert help. Anyone?

Checked my version of php via the web and got this message when trying to view whichphp file:
Access denied for user 'apache'@'localhost' (using password: NO)
Do I have some kind of permission problem which is causing me not to see any pages? I do have php 5.1.6

[UPDATE] All fixed now. Ran checksum, replaced all the files that were missing from an full install instead of an upgrade. Then went to upgrade folder and completed the steps.