Diff machines burn differently?!?!

I’ve been using an old 750mhz Duron to burn files to DVD
using Nero. So far, 600 discs, all play on my two stand-alone DVD players, one high-end Sony, one el cheap.
However, I switched to an Athlon machine 2800mhz, same
DVD burner, a Sony and the disks will not play on my
stand-alone players. What gives??

Make sure the burnt disc is being finalized or not being burnt in multisession.

I’ve always used Nero Smart Start and left it up to it
as to the settings. I checked them and it was set at "max speed"
for burning which is 16x (Sony). The disks I started using (always
stupid to change two variables when trying new things) are new
4x discs ($12.00/100 discs) and the new machine. I’ll do some
experimenting with different settings and see what happens.