Could well be your modem.
USB ADSL modems are well known to cause problems
with Macs, especially sleep related problems.
I use to have an Alcatel jobbie
that used to give me kernel panics (the multi-lingual grey screen you're seeing) on a
regular basis.
I've had a recent Powerbook for almost a year now and have never
had a single crash (well, apart from Logic!)
Best bet is to dump your USB modem
and get a wireless ethernet one, available for about £50 now. Once you try wireless
you'll never go back.
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My Space