F451

Dear Forum I am at my wits end trying to determine why my computer using XP Professional edition (final version) will go thru the boot process one moment without any problem then the next time I boot it goes thru the process but locks mid-way before the complete boot process? The boot failure when it happens is like this: after lock up I cannot manually re-boot with the switch and the power button does not work nor cntrl alt delete/2x.? Is this a hard-drive problem a software problem or a DOS system problem. I would really like to know before I take it to the computer shop and the sharks there try to tell me its a hard-drive problem just to sell me another hard-drive (Maxtor). Please I would appreciate anyones advice. However since my system is unstable could you please send me a reply by email as well as a posting? Thanking you in advance F451 :D