I am a beginner and just starting to explore the possibilities of Bitcoins. So I would be very grateful if somebody could help me with this question. Is there a risk that my Bitcoins are lost if the PC with the bitcoins resp. with the Bitcoin wallet stored on it is stolen or has crashed? Thank you very much.
Accessing to (your) bitcoin requires a private key. This is kind a long number password to access the bitcoin on the network called blockchain.
All bitcoin are saved in this (online) network.
A private key looks like this:
Important thing is you save your private key on different places in case you need it back again. One good practice is print it on a paper with QR code. This is called Cold Storage. This is your backup.
Don't show this private key to anyone else and save a copy somewhere else than your home.
Act like a bank, because with bitcoin you are own bank. When your PC is gone, you take the private key and setup a new wallet on a device. Amount of the bitcoin will be exactly the same as it was left last time, because it is saved on the blockchain.
Read more here https://en.bitcoin.it/wiki/Private_key