First what Windows OS and what version of XAMPP are you using?
shinokada wrote:I was using it whole day today. However tonight, it suddenly stop working.
What suddenly stopped working - error messages, error.log file etc.
shinokada wrote:What's wrong with it? Is it because Windows' update?
No idea unless you tell us and if it was a Windows update then check your Windows Firewall settings and possibly do a reboot.
shinokada wrote:Do I need to install it again?
I doubt that would help but without you provide some details of what is wrong then to make a suggestion could only be a guesswork.