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Here is suggested workaround for Windows XP:
You may need Switch to Mac if you already have a PC and want to migrate it to your Parallels Desktop.
If you want to make a fresh...
1.You could log in on parallels.com and find your keys on https://www.parallels.com/account/products/ page or
2.You could contact support by...
Most reasonnable solution for you is to reinstall Parallels Tools: Virtual Machine -> Reinstal Parallels Tools.