Why is my PRAM screwy?

I have a 4-yr old Macbook pro which is 99% of the time run on the power adaptor. Today all of a sudden when I try to turn it on I got a weird symbol on start-up and nothing would happen so I followed some advice and reset my PRAM but now everytime I close the lid or restart I have to reset the PRAM again. I’ve searched for answers but couldn’t find any help. Most people with a similar problem were on relatively new computers. As you could guess, at 4 years it’s out of warranty. I’ve made no major changes to the system as of late. Please help :(