Maybe it's time for a redesign. On the internet, things change rapidly.
Customers expect businesses on the internet to also change rapidly and adapt.
It gives the customer confidence that he or she is dealing with a reputable company that is interested in keeping their internet business thriving. Arriving at a website which looks like it hasn't been changed for years gives the customer a sense that the website isn't inhabited. Sort of like arriving at a ghost town. Customers see this and wonder if you're still in business. They may look around a bit, but they aren't likely to buy with confidence if they buy at all.