macro help: click button to update value of primary cell

Hello all,

I was not able to locate what I need in anything already posted, so here goes...
I am wanting to create macros (but don't know VBA) to assign to buttons such that clicking the button will change the value of a primary cell, but not below 0. Some details:
* primary cell will be G7 on worksheet 1, with a starting value of 25
* one button on each of the other 4 worksheets in the same workbook, with values of -3, -1, +1, and +3 (respectively)
* clicking a button will add/subtract the button's value from G7 (worksheet 1)
* the value of G7 can not fall below 0 (value of 0 is okay): if clicking a button should cause G7 to go negative, a message appears "Not enough points" and there is no change to the value of G7

Not sure if this is possible, but I'm confident that this forum can find the answer if it is. Thank you in advance for your time and assistance.

Thank you so much! I'll plug it in as soon as I have access to the spreadsheet, then I'll let you know.

works beautifully - thanks again.