Entering values into the 'Account', 'Company' and 'Department' Value Set, the Qualifiers field is blued out making it impossible to input qualifiers for the 'Account' value set. How do I overcome this problem please?

Are you talking about Account Type (Asset,Expense etc) qualifiers on the Value screen?
This happens when you create your Account value set and start entering values into it without first attaching it to a segment in your COA structure.
This is what you should do:
1) Create your COA structure. If it is already created make sure it is unfrozen.
2) Make sure your value set is attached to the Account segment in your COA structure.
3) Freeze the COA structure.
Now verify if the account type qualifiers popup in your Values window.