Thanks for getting in touch and sorry to hear that you've been having issues with your Tivo box Babsnsarah.
Is the box slow and unresponsive when loading menus or is it just when you are using the remote control to change channels and enter a pin number as you stated in the original post?
I know this is a silly question but have you replaced the batteries in the remote recently? The performance of the remote control can be affected, when the batteries are running low and maybe the cause of this issue.
How much memory do you have left on the box and do you have a lot of recordings in your suggestions folder? If the memory is low this can also affect the performance of the box.