Hi Suzanne,
Check the little laser on the bottom - sometimes it gets clogged with debris.
Be sure you have the latest drivers :
Wireless Mobile Mouse 4000
http://www.microsoft.com/hardware/en-us/p/wireless-mobile-mouse-4000/D5D-00001#support
Troubleshoot a wireless mouse that does not function correctly
http://support.microsoft.com/kb/321122
Wireless Mobile Mouse 4000 - has a 3 year warranty
Microsoft Hardware Warranties
http://www.microsoft.com/hardware/Warranties.mspx
These mice come with 90 tech support from day of 1st incident which would start when
you contact Microsoft at the below number.
MS Hardware Support and Warranty Claims
Tech Support 1-800-936-5700 for MS Hardware or 1-800- Microsoft 1-800-642-7676
Hope this helps.
Rob Brown - Microsoft MVP <- profile - Windows Expert - Consumer : Bicycle - Mark Twain said it right.