Direct to disc recording

[r.erorr]

I have had experienced strange behavior while recording direct to disc. When I recorded 10 racks 4 ch, that is 10 audio files (4 channel) ~ 13 min long (~750 Mb x 10). First ~5-7 min goes fine, but end part ~10-13 min have strong delay with rack volume. I make same smooth fadein's and out's, but recorded files have robust and delayed like on/off volume effect.
I have i3 acer (quad core, 2.6 Gh, 4Gb) that is not very powerful Pc, so maybe this is hardware problem? but if . . what exactly?