Take you new PC (or existing one) to a PC guy and see what he thinks. It generally only cost a couple dollars more to have a PC guy build you a PC, without all the bloat (programs/software) that screws with the operating system. New PC's with Microsoft (windows) operating system, will have all the security you should need to keep you safe. If you do alot of internet stuff, get a seperate cheap system for internet personally surfing only. Keep your good PC for your record keeping and maybe internet banking/personal ONLY. That's a very secure way to keep others from your accounts . . .  . ..
ETA: Oh, on the PC hardware side - Do you keep it clean ? Blow out (or vac) the inside/guts from time to time. Dust build up on hardware adds heat and heat is the killer of pc's . . . ..