Please report what software version is fitted - the SW version is shown on the top right hand corner of the main Settings screen, and will appear as numbers like "3-1/63" or "4-1/00"

Issues that can slow down a navigation computer:
1. Dirty or scratched navigation disc - dirty discs have more read errors, this slows down disc access time, and makes nav unresponsive. Remove disc and ensure it is clean and scratch-free.

2. Old or weak laser - creates same problem as in #1 above. SOlution is to replace laser or complete disc mechanism.

3. Mk3 nav - the Mk3 nav is simply not that fast.
If you have a Mk3 and want a speedier nav, consider exchanging it for a Mk4, which is much faster and more responsive.