Plot greying out

Hi I hope someone can help me as I can find the answer to this problem.

I have a particular file which wont print correctly. Its like it has a transparency layer, only prints in feint greyscale.

I have tried printing direct to the printer, via pdf, even copying the work into another drawing which I know prints just fine and nothing is working. Its a particular problem as the plans are for an elderly couple.

Using windows 10 on PC

Any help appreciated, many thanks in advance