What size, and how were they created?
I have read that files that are too large can cause problems
I have also read that some digital cameras add extra, proprietary, information in the file header that can cause problems
Opening the file in Photoshop (or other editor?) and resaving under a new name will usually fix the 2nd possible problem
Did you do a complete wipe of your harddisk and a fresh install of Win7? If not, that is likely the cause.
The files are not large in size or pixel dimensions, and they worked fine previously.
Also I did a clean install on brand new hard drives.
I have also tried renaming/ resaving the files but that also didn't help.
And yes they were created with Photoshop CS4
This is weird. I've never heard that problem, so maybe a repair install is worth the effort.