blank screen

i have recently purchased a new laptop (vista hp pre installed) i am not
having too many problems and generaly find it good considering its a new os
but after about 4weeks of daily use when i boot up it gets to the welcome
screen fine and i log in ok but then the screen goes black for about 3 mins
..I have done all the usual i.e selective startup,disabled unesesary
services,uninstalled programs..ect but still have this problem does anyone
know if this is normal ihave read on this forum that superfetch can cause
similar problems but ihave disabled that to no effect any suggestions will be
appreciated. if its not a problem but normal i would like to know so i can
stop curing a problem that doesnt exist
on a slightly different note having read about the problems some people are
having with vista being slow i have got rid of all unnessesary pre installed
software ,dont use areo and spent allot of time configuring and it runs
really well
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martyb