Bitcoin downloads transaction data:
The Bitcoin software keeps track of all transactions in a pool of data. In order to verify transactions you need to download that data before you can use the Bitcoin software
Downloading the data can take hours, so you should let your PC run for a while.
Here’s a screenshot of what it looks like – at the bottom there should be a green bar
Even if you have a good CPU, the Bitcoin software might put a strain on your hardware
In some cases, the CPU won’t be fast enough and you will run in lags, freezes and blue screens. In that case you can either try to overclock your CPU or get a new one, both options will take time and money.