Possible Duplicate:
Difference between shutdown ( power off ) and restart ( reboot )
When I shutdown my Windows PC sometimes the boot time increases to 150% of the fastest boot it ever did. But when I reboot my PC, the boot is always as fast as possible.
What's the difference between a reboot and a 2-step reboot (shutdown, and the turn on again)?
Is there any way to force to do the slowest reboot mode?
99% of the time the difference is purely electrical and makes no difference to anything in the software one way or another.
Depending on your motherboard, the POST process on a warm reboot may be different - it may not do the same initializations on video and network cards, may not run the same memory tests, etc...this really varies from machine to machine but is probably the reason for a lot of the discrepancy that you're seeing in your particular machine. Without knowing specifically what it is I'd hesitate to conjecture as to what settings might achieve your goal - I'm sort of curious why you'd want to slow it down anyway?
It's also possible that your hard drive just spins up from a cold start REAAAAAAAAALLY slowly, but it would have to be damned slow to make that much of a difference in boot time. But it's certainly possible.
You might also see here and here for a little insight as to specifics.
