If you suspect that your Windows system has been compromised by a crack, you should take immediate action to secure your system. First, disconnect from the internet to prevent any potential spread of malware. Run a thorough scan using a reputable antivirus or anti-malware program to detect and remove any threats. It is also advisable to back up your important data. After cleaning your system, consider reinstalling Windows using a legitimate copy to ensure that your operating system is secure and functioning properly. Contacting Microsoft Support for further guidance can also be helpful.