Cannot read dvd-r's

jjames_3

Very likely the 8x Ridiscs are made by CMC, whereas the 4x are Ritek.

Ritek media has a reputation for being readable by just about any player, CMC is less good in this respect. You'll be able to verify this as being the case by looking at the underside. The 8x discs will have a 4-digit numeric code stamped in the centre (the one I have here is 0320), the 4x discs will lack this code. That code is a giveaway that the discs are manufactured by CMC.

It's highly likely that this is normal for that model of DVDROM drive. In future if you buy discs that the supplier verify are manufactured by Ritek you should be fine.