CRM is not functioning correctly - can't create new lead or contact, etc.

CRM is not functioning correctly - can't create new lead or contact, etc.

Hello
Thank you for the use of this program.
I have been using the CRM for several months with no issues at all.
Today, nothing is working as it should.  I can't look up a client; can't add new lead or contact; can't see all my existing contacts even, etc.
Would you be able to investigate the issue asap please?
Again -- THANK YOU!!