Yesterday I installed Windows 8 Customer Preview from the DVD, but was not prompted for a product key. It keeps telling me that its not activated and will expire tomorrow! When I click the Activate "button" in the top-left of the Control Panel screen, nothing happens.

any other have the same problem?

When you downloaded, you would have had, at some stage, a product key shown. I am not clear as to how you even managed to install it without, as you cannot get past the box in the early part of the install, unless you do so. But, reading your post. Do you mean the developer preview, or the consumer preview? I am referring to the latter. (There is no such beast as a "customer" preview.

Microsoft has published two keys that anyone can use.The ISO download page includes this public key:
DNJXJ-7XBW8-2378T-X22TX-BKG7J
The Windows 8 Consumer Preview FAQ has a different key:
NF32V-Q9P3W-7DR7Y-JGWRW-JFCK8

Hello Dave. I decided to try this forum as well.

I believe this OP will have to reinstall Win 8 CP in the correct manner. He definitely should have been prompted for the key and since he was not he did something wrong. I would suspect he downloaded the DP not the CP which is now out of date.

I would suggest downloading again from an approved site. I am unable to supply the site URL since my post count is less than 50. Sorry you are on your own there.