If it worked recently try doing a system restore to a few days before it stopped working. If that doesnt work please tell me what software you are using and give me the exact error message word for word completely and at what point you get the message please

SYSTEM RESTORE INSTRUCTIONS - XP VISTA
start menu / all programs / accessories / system tools / system restore
select restore to an earlier date

you will get a calendar with various restore points for each day

choose one for a date BEFORE the problem started

hit the ok /restore button

the system will start to shut itself down and a blue status line will come up in a box saying restoring your system settings.

when it finishes the system will restart itself.

hopefully everything will work the way it did on the date you selected

a system restore as i told you to do it will not affect your data at all. It only affects program files and system settings.

If you dont want to do that than you need to reinstall the quickbooks program itself

QUICKBOOKS CLEAN INSTALL

try doing a clean install with the instructions on this page. It should not effect your data but i always recomend making sure that you have a good back up and / or a copy of your data file ( it ends .qbw ) in a safe place such as a flash drive or another folder.

It requires that you have a copy of the quickbooks install cd or download. If you downloaded from intuit you can get another copy free.

If you purchased from Intuit directly you can download again for 3 years.

For quickbooks go to https://www.intuit.com/login/

click on cart orders downloads

sign in with your intuit id and password. ( usually your email address is the id )

click on downloads and unlocks

That should give you a list of any intuit product that you purchased online within the last 3 years with a download button.

This page has complete instructions for the uninstall and reinstall INCLUDING a clean install utility that you want to download and run.

http://support.quickbooks.intuit.com/support/Articles/HOW12212

I will continue to help you until we get it solved. Please just post back your reply. Every time you hit "needs more help" it gives me a negative rating which is a new thing the site hasnt got worked out yet and i wind up with a bunch of negative ratings on a single question that often gets resolved with 1 good rating at the end. But i am still stuck with a dozen negative ones. Please just post and dont rate me until we are finished. Thanks

Make sure that you are logging into windows with an administrator account. What operating system are you using ? If that doesnt work and reinstalling doesnt work there is a folder that you have to delete. Exactly how to do it varies by operating system

This is for xp

1. Right-click the Windows Start button and select Explore.
2. Select the Tools menu and select Folder Options.
3. Click the View tab and clear the Hide extensions for known file types checkbox.
4. Select Show hidden files and folders and clear Hide protected operating system files (Recommended).
5. Click OK.
6. Navigate in the left window to the location: C:\Documents and Settings\All Users\Application Data\Intuit\Entitlement Client\v6.0. To navigate, click the plus sign (+) next to each folder listed.
7. Right click the first file in this folder and select Delete. Click Yes and repeat for each additional file in the v6.0 folder.
8. Open Point of Sale again and complete the registration process again. If the error persists, try solution 2.

Methods for other operarting systems are on this page

http://support.quickbooks.intuit.com/support/articles/SLN40328