Have you checked the batteries?
However, give the CRP series a new home in the bin and then buy a Jepessen CR type eg CR5 or CR2. There's even a CR1 that's big enough to make a good frisbee. My CR5s have worked perfectly for Oz, USA & UK ATPLs. Alternatively, Kane used to make excellent slide type
As for why have them, they don't need power (apart from light to see them). In many circumstances I can derive answers faster on my whiz wheel than through using a calculator of some sort.
Another advantage, they also force the user to confirm the answer with a 'reasonable-ness' check. Calculators
tend lead people to accept whatever shows on the screen.
Last of all, if you can use the calculator side of any of the whiz wheels, then you will know what the bezel on your big pilot's watch is for!!