Using an Event Change

Hello

I would like to lock a range of cells based on the contents of a single cell. In Cell C6 the user is expected to select either "Acquisition" or "Renewal" from a drop down list. If they select "Renewal" I would like to lock both cells C7 & C8, and if possible add some conditional formatting that would change the background color of the cell. The trouble I'm having is that in cell C7 there is a drop down list, and cell C8 a VLOOKUP formula which seems to complicate things..

I am a total noobie to VBA so any help would be greatly appreciated.

Thanks!