Start the software, then use the VirtualDJ browser to browse to where your music is located. Once you have restored your database, install the latest VirtualDJ v7.0.3 from your Download Center. Please see backup database & settings and backup music collection. You should always backup your database and music collection on a regular basis along with any other files on your computer that are important to you. If you do not have a backup, then unfortunately you will have to start again from scratch.
Please see Simply restore your v6 database from your backup. There have been many bugs fixed in the latest version as well as many new features added. Are you still using versions prior to v6.0.5? We have been on v7 for some time now and the latest version is v7.3.
Always wait until you have plenty of time to install and test the update (If you DJ at weekends only, then Monday is a good time to do this.) Also, this thread is over 2 years old and is for a very old and out-of-date version of the software. You should never make any changes to your system just prior to going to a gig.