I have a 4 year old Wytron DVD 399 duplicator that was built for our school. It is a tower that originally could copy seven DVDs at a time. The first year it copied both -r and +r DVDs with few problems. The second year the fourth copier stopped working. I have only copied about 500 dvds for school projects throughout the years. Last year it stopped using Memorex DVD's but would use TDX. This year it starts to copy but then fails. Our school is on a limited budget. What could be the problem and what could be a cheap solution?