has anyone exprienced the following problem?

I have a long show with probably over fifty different
clips. just recently after the show got pretty big, I've
noticed that some clips show up with only a white
thumbnail, and when I play them, there is nothing but
silence and black. It's like vegas thinks the clip is
offline, but it doesn't say that it is offline.

also, at the same time when I drag some clips from the
media explorer window to the trimmer or timeline, only
audio information will paste in even though I can view the
whole clip with windows media player.

the wierd part is that after rebooting, the artifacts will
come and go, and the clips that are affected are not always
the same clips...

Any suggestions, or does this sound familiar?

my system is:

PIII 733
128 MB Ram
20 Gig IBM/66 ide media (separate system drive, both
freshly defragged)
DFI mainboard/VIA chipset
SIIG 1394 card
etc...

jeremykorb@yahoo.com