My tablet toshiba excite pure is saying Unfortunetly, sysyem UI has stopped. It goes off when i push ok and comes right back. How do i remove it?

Have you tried to wipe the cache partition

App data

Step 1 Press the "Menu" button and tap "Settings." Touch "Applications."
Step 2
Tap "Manage Applications," select the "All" tab and touch an application name.

Step 3
Touch the "Clear Data" button to wipe the app's saved data. Tap "Clear Cache" to remove any cached data for the app.
Phone Data

Step 1 Turn off your Android device. Reboot the phone or tablet into Recovery Mode. The process is specific to the device model. For the Motorola Droid, press and hold the "Power" button and the "X" key on the slideout keyboard. Release the "Power" button when the Motorola icon appears. Press the "Volume-up" and "Camera" buttons simultaneously to open the Recovery Console. To access Recovery Mode with the LG Ally, press and hold the "Power," "Home" and "Volume" buttons simultaneously.
Step 2
Press the "Volume-down" button to scroll to "Wipe Data/Factory Reset." Press the "Camera" button to select it.
Step 3
Scroll to and select "Wipe Cache Partition."
Step 4
Highlight and select "Reboot System Now."