I normally reply by saying that I was glad they had called because it takes ages for my PC to boot up!
On being asked to boot up I tell them to stand by whilst doing so.
I then start to cut the grass or carry out some other menial time consuming task, popping back to the phone every five minutes. I say "Are you still there, I did tell you that it took ages to boot up!"
After about 30 minutes they give up!!
.......and keeping them holding on stops them calling other people!!