Is this normal? Definitely not.
Have you made any changes to the site, recently? What type of site are you running? MySQL?
It certainly shouldn't take all day to reboot your server.
Have you addressed this with your DC techs? Have you had your admin look at this?
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I know it may sound silly, but every time the server crashes, is it the same legnth of time that it has been on? I would then suspect a bad or intermitten shortting power supply. (yes i've seen it happen before)