assuming you follow normal computer "hygiene" , from your description below it is hard to say what if anything is wrong with it.
open it, clean it (blow with compressed air), primarily to prevent overheating . what you describe with delayed boot/audio glitches could be driver issues (i.e. system assuming earlier gen drivers when trying to run new OS).
install, run antivirus, they are dirt cheap (<$10)
find the manufacturer of your hard drive , get their utils, run them for safety measure
go to Dell, punch in support tag, look at recommended downloads in general (bios, firmware) and for your OS in particular. do you run the right drivers?
look into event log , what does it says when crashes happen? do you get crash dump files generated, etc.
I do not know what you do on that machine or how important for it to stay up (how critical is to say be without it for few days or the week). generally for me - 'if there is a doubt, there is no doubt' , I would pitch/donate/discard/store the system I am not sure at and get something I can trust if I can not tolerate significant 'computer downtime' (use it to make money by working remotely, etc). I would not be buying any laptop parts , there is very limited if any upgradability/replacebility, installation is cumbersome, and these things by definition are disposable.
if you want to have the features of easy replace ability, a desktop would serve you so much better and be of much higher value. a lot of people who insist they need to have laptop use them as very bad desktop, rarely if ever moving them. ..