Please Help: dvd and divx info please

hi there, ive been racking my brains and searching the net frantically. could someone please help me. ive had nero for about a year and everything was brilliant with it, burning any kind of discs was no problem. i didnt bother running off any discs and turned my internet off for a couple of months. wen i was reconnected i tried to run off a dvd video through nero and it wouldnt work. i tried using the same projects that i knew had worked for me before and it wont work. it stiil does cd and mp3 but not dvd video which plays without problem in all my dvd players. so i checkd on this and it seems alot of people have this problem, so i tried other free downloadable dvd burners such as burn 4 free but i cant get a film over 700mb onto a disc where as nero could. so now ive bought a divx player so i can run off discs with more films on them. can u tell me why certain things still wont play on it. i put 6 films on one disc using divx player on my computer to run off a disc. why do i keep getting these problems? please help