Blank page when accessing Gallery

I have been having problems with the Gallery link just producing a blank page. The first time this happened my web host company restored files and this seemed to fix it. However, the next day it was gone again although the files were there. They restored again but asked me to upgrade to Gallery 2.3 - which I have done - and change all passwords - done. I loaded in some 60+ more pictures and all was well last night. Today, again, I just get a blank page. When I look at my directories, they all 'look' fine although I don't know every file that should be there. I don't know if this is a problem with Gallery or my Web host but their only solution seems to be to restore. Any other ideas I can suggest to them?

Thanks Dave
We have checked error logs and nothing shows up. I saw the reference to resources but felt that as I had seen everything working fine after loading in the last bunch of photos, that this wouldn't be the problem. I'll work with the server group to see what can be found noting your points.

Thanks again
I still haven't a running Gallery and this is due to a long history - which I will try to keep short. My website has been infected - by Gumblar - all passwords have now been changed and my host has cleaned my files - such that everything seems to be working except Gallery. Within Gallery I have found multiple instances of eval(base64_decode).... which translates to Gallery type info with another base64_decode embedded. That part translates to a Siva4kids.org site which we find is a Gumblar lookalike site ...etc. etc. I have found multiple instances of this string also in new files (called gifimg.php) in each images directory and have deleted them and have cleaned the string from config.php and index.php. My top level g2data directory has a range of permissions but under it I have another g2data directory with all 777 permissions as you say I need.
I am inclined to scrap the whole works and start again but don't want to lose all my albums and pictures. I saw reference in your documentation to an upgrade and an install URL under http://www.example.com/gallery where I can check my files but I get a 'FILE not Found' message when searching on these. I have put my gallery in debug mode - ottawaoc.ca/gallery - and get the message 'Warning: Cannot modify header information - headers already sent by (output started at /home/ottawaoc/public_html/gallery/index.php:1) in /home/ottawaoc/public_html/gallery/modules/core/classes/GalleryPhpVm.class on line 142'

Can you recommend a plan for rescueing my gallery - hopefully without too much lose of data. It was upgraded last week through Fantastico but Fantastico does not give me any option such as re-upgrading.

Thanks