Well this sounds like a hardware problem then. On the other hand 3+ years of usage for so badly built calculator is quite long time. I'd just dump it.
Yeah, the build quality wasn't great. And the screen drivers were wrong when I first got it.
But you have to admit the colour scheme was attractive and easy-to-read.
Any advice for convincing HP that it is in their interest to give me a discount on a 50 to replace the 49?