Slow start up... as in window start up loading screen? Or after
u login window then long start up?
If its the first, ur HDD dying...
If it's the latter, ur lappy might be infected with
spywares/adwares... go clean them...
Btw, ur title kinda funny, "Laptop keeps hanging
unexpectedly"... does laptop hangs expectedly??? 
After logging in then slow liao.
Suggest the title lor! =D