Quoted:
1. Choose a reliable brand.
2. Make sure the model you choose isn't junk.
3. Make sure you are getting decent hardware; sounds like you don't do anything gaming/video editing/photoshop so all you really need to worry about is a fast CPU, 6GB of RAM, and whatever size of HDD space you require. Possibly an SSD if you don't need much space. SSD = far faster and less likely to break than an HDD, but costs about 10 times as much per GB.
4. Download Microsoft Security Essentials, Malywarebytes and Spybot S&D.
5. Don't go to shady torrent websites.
6. Don't click on spam email.
7. Scan with the above programs every now and then. Current CPUs are fast enough to run this in the background while you do other things so there is no reason not to run them.
8. Download Crap Cleaner. Run the Cleaner and the Registry Cleaner every week.
9. If you have an HDD, defrag it every now and then.
10. Buy an external HDD. Make backups of data monthly. Buy DVDs. Burn data DVDs every now and then.
If you go with Apple:
1. Get ESET anti virus. It is free though not as full of a program when compared to MSE.
2. Don't go to shady websites, spam email ect.
If you suspect your PC is having issues:
1. Download CPUID Monitor. This will display your component parts. You can see if something is over heating.
2. Download HD Tune or Crystal HD. You can scan of issues of your HDD here.
this, most definitely the best advice in this thread. my parents cannot seem to grasp the concept that the internet is a place full of malicious intent with regards to computer integrity and personal information.
porn sites are a huge killer too. if you're not internet savvy enough to keep your computer clean, this will be the biggest source of viruses you can get aside from downloading things of questionable origin.
also, download your windows updates regularly as they contain lots of security fixes.