It is an ATI Catalyst problem. My ticket at ATI Customer Care:
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Product: Radeon 9600 PRO 128MB
Driver Version: CATALYST 5.10
Summary: Switching DVI monitor off and back on makes screen disappear
Details: When I turn off my Samsung 214t DVI monitor and turn it back on, the...
Yeah, the 214t is pretty nice.
But the 'losing DVI signal when powered off and on or switching digital/analog/digital with ATI drivers' is really pissing me off.
It is definitely an ATI driver problem (using cat 5.10). Uninstalling those and using windows default drivers made the problem go...