"Detieorate" is not quite the right word, but, yes, if you have not used your racquet for a few years, you will need to re-string it before you play. Otherwise, the strings will feel dead.
Over time, strings lose their resiliency: their ability to spring back into position while hitting a ball. There are several things that cause the loss of resiliency: hitting balls, the bending of the frame during play, the expanding/contracting of your frame and strings through warmer and colder days etc.
As such, you are supposed to re-string a racquet that you are using regularly as many times a year as you play in a week. I play 5-6 days per week, so I re-string about 5 times per year.
In your case, your strings will have lost their resiliency because for several years they have been held at a tension of 50-60 lbs. That, alone, will deaden the strings.