I am working on a pic using layers , I used a mask to create a sky color gradient. I then tried to erase parts of the mask and I can't open up my layers anymore. When I click on a layers it just goes a darker gray, instead of the normal blue color that shows a layer being worked on. also a waring pops up that says " could not use the brush tool becuse the target channel is hidden" any help would be great.

Try trashing the preferences.

Shot down photoshop then when you restart it hold down the Shift-Option-Command keys and you will get a box that asks Delete the Adobe Photoshop Setting files click yes.

This has worked for me.

Won't that make me lose the image I've been working on?

I do NOT recommend you reset your preferences, except as a last resort. They do not get corrupted very often and the problem you have does not sound like corrupted prefs file.
First thing I would do is Image>Duplicate. If you have turned something on or off or have a single channel or mask activated, it shouyld reset when you duplicate the image and you will not lose anything.
As for the image you were working on
Things to check:
- That you have not accidentally turned off any layer icons (eyeballs)
- Check to be sure that the layer you are trying to brush is actually the active layer
- Verify whether you have selected the layer pixels or the layer mask
- Check the 4 lock buttons near the top of the pallette.
The error msg you are getting typically refers to some state that you have put your image in which is preventing the layer from being worked on because it is considered hidden.
Regards, Murray

You probably don't need to reset the preferences here but to answer your question, "No, resetting the preferences won't mean losing the file you are working on as long as you saved it before quitting and restarting Photoshop."

I think what you have done is hidden your layer's visibility by inadvertently clicking on the eyeball icon. This is why you are getting "Could not use the brush tool because the target layer is hidden." warning. Make sure that the 'eyeball' next to the target layer is visible. If you are not sure what I mean look at the attachment.

Sincerely Syd

Syd almost got the point. The error-message tells it all: could not use the brush tool becuse the target channel is hidden

Unhide all channels in the channels palette and the problem should be gone. If it isn't, could you post the psd-file?

thanks for the help, I'll try it out this afternoon.