There may be several causes for this. To troubleshoot follow the steps below: [1] Does the instrument come on if the AC adaptor is attached? If so then the AC adaptor is most likely good. You can confirm this with a voltmeter. All AC adaptors have a rated DC voltage printed on their identifying labels. If your adaptor is rated at 12 VDC then a quick test with a voltmeter will confirm. [2] If your AD adaptor is found to be good then either the instrument's power connection has been damaged or the batteries themselves are bad. Most X-Rite instruments have replaceable NiCad or NMH batteries. In many cases they are discrete AA cells in other cases battery packs that must be replaced as a unit. If your instrument uses the AA batteries, then you can generally purchase replacements at stores such as Best Buy or Radio Shack. Always purchase the best quality batteries that you can find. The more milliamps/hours in the battery specification the better. Today's super NMH batteries can be rated at nearly 3000 milliamp/hours. [3] Assuming no physical damage to your instrument, the replacement of the batteries should return you to normal operation. If this fails, however , then the instrument will need to be serviced.