Hi anzprad,
Your mode button may be sticking, and not making proper contact into the switch on the movement. Try lightly spraying compressed air around the buttons, then, either electronic cleaner, or silcone spray around just the buttons. If that doesn't help, you may have water damage from moisture encroaching into the case from a leaky seal. Be sure to clean off any excess spray with a soft cloth.
If that doesn't help, contact Casio at the following numbers (if don't you have this info already):
For Repair support in USA at 1-800-706-2534 during regular business hours (currently Monday-Friday 9:00a.m. - 5:00pm EST, Saturday / Sunday 10:00 a.m. - 8:00 p.m.)
For Technical support in USA at 1-800-435-7732 during regular business hours (currently Monday-Friday 9:00 a.m. - 8:00pm EST for all products, Saturday / Sunday 10:00 a.m. - 8:00 p.m)
For Customers in Canada at 1-800-661-2274
Let me know if you still need further assistance.
Regards, Bill