Slow start after hiybrid sleep and power down

My Vista-SP1 PC starts rather slowly after it has been put into hybrid sleep
and the mains power has been down. This is strange as it starts quickly after
pure hibernate, what should be the same.
Start times are as follows:
Hybrid-Sleep (mains power on stays on): 15 sec
Hybrid-Sleep (mains power has been off): 120 sec
Hibernate: 35 sec

Remarkable at the start after hybrid sleep (+power down) is that the screen
is black for a long time (only cursor visible).
It is not a blocking problem, but annoying (and strange as hibernate is ok)

It is a recent PC (Vista SP1, Core 2 Duo E8400, P35, 4 GB, HDD WD 640 GB,
graphics Asus 3850)

Advice to solve this is welcome