there r 3 possibilities in common for slower boot.1st low system configuration 2.loads of programs at startup.3 virus attack.
few steps that might help u.
1.make sure ur system is virus free.{using kaspersky immediately after system format does best}
2.remove unnecessary programs 4m start up.u may do it 4m d program if d option is there or click start,run,type "msconfig" n hit enter.under d startup tab,uncheck all those programs tat u feel like unnecessary.caution:some of them are those tat runs d os.b careful or u may end up wit unnecessary results.
3.download a free microsoft tool viz.bootvis.download link
http://download1us.softpedia.com/dl/2c7fe73c6421d13cb5253d8aeff6a3a3/48995ec6/100003465/software/system/bootvis.msi
run d program.under "trace" click next boot+driver delay.put 2 in number of repeatition and ok.ur system will restart 2 times.just leave it idle til d graph comes.now again go to trace n hit "optimize system" this time.it will again restart ur system.again wait 4 some time till boot vis optimizes ur system.{it puts ur boot files one after another making the system to find it early resulting a faster boot}
4.defragmantation.
these r few things that mst help u.if its still not helping thn i guess its time 4 a system upgrade. :)