Is there a way, using formulas, or validation settings to restrict entry in
one cell based on what is entered in other cells?

Example. If values in Col A are less than 3, I would like the user NOT to
be able to enter ANYTHING IN col B. IF values in Col A are 3 or more
however, I would like the user to have a choice of two other ratings...say
High, Moderate. so that final data could look something like this:

A B
4 High
1 BLANK (this cell would be restricted)
5 Mod
2 BLANK (this cell would be restricted)
3 High
4 Mod
5 Mod

THank You!!!