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Which computer model is the best to buy? - computer model itchy eyes

My 4 years old desktop, HP has broken last week. I know nothing about computers. I need a new computer without the monkey for less than $ 400,00. Good ride, good memory. I do not know the difference betwee AMD and Intel, but either works best. Suggestions?
If you use a reliable model you recommend. I use it for school, not to play.