You may try (I assume your Note has been updated to ICS):
1). go to settings–Pen settings–Dominant hand, change it to left handed, then change back to right handed, and see whether the screen responds to the S Pen.
2)if not, change the screen rotation several times, to see whether the screen responds to the S Pen
3)if not, go to settings–Display, try horizontal calibration ,and Gyroscope calibration
4). if still not working, go to local Samsung service center, or vendor”s shop for a check or replacement.