Layer effects not sticking in Photoshop

Hey all,

While it's not strictly art based, I desperately need some help.

I have a line-art image that was scanned in as an 8 bit tif file that needs to be darkened. Normally I convert it to Greyscale, tweak it and convert back to bitmap (which it needs to be to use in AutoCAD). However, for some reason the tweaks are not sticking. So far I've tried;
1) Duplicate layers set to multiply (which has worked in the past)
2) Brightness and Contrast
3) Converting to RGB and trying 1 and 2 above
3) Saving as a jpeg and trying 1 and 2 above

However when the layers collapse the effects simply vanish and I'm left with the original, or at least something that looks exactly like the original.

I've tried rescanning but the same thing happens, so I have a suspicion I've inadvertently toggled something on or off.

Any help would be greatly appreciated

Infinatepixel / Zinc

How about instead of collapsing you use CTRL+SHIFT+ALT+E which will create a composite of everything visible into a separate layer above everything. Then any effects/alterations you made to the previous layers will be baked into a layer.

Still no joy I get the progress bar along the bottom of the screen but the layer filter just changes back to Normal.

I'm beginning to think it may be my dottery old version of PS 6. I've just tried adjusting the curves and the preview looks fine, but when I hit OK it doesn't do anything.

How about trying a different image format?

I've tried converting it and saving it as both jpeg and psd, but the problem persists.

Definitely something in this file/file type though as I've just successfully applied multiply layers to a different image.

I vaguely recall having similar problems with some files in Photoshop 6, but that was ages ago so I don't remember what I did to fix it. It might have been something as simple as clearing out temp files.

I could take a look at the file for you if you are able to upload it somewhere.

Thanks for the offer Banj, but it's for work so unfortunately I'd get my fingers slapped if I upload it.

The thing that's bugging me is I've gone through this procedure many times before and it's worked fine. I'll try another reboot and some purging and see what happens.

Thanks for the help though Banj, appreciated.