there is also the remote possibility that the OPs laptop got some data corruption and the private key is not correct due to that. that's probably very unlikely but i guess it is a remote possibility.
But considering OP received the private key via email and most people use third-party email provider, this should be impossible.
no one should be needing to buy bitcoin from someone else using paypal these days though. since they can just buy it from paypal directly.
I agree, although IIRC option to buy/sell cryptocurrency isn't available on some country.