where does MySQL store database files?

In any case you can know it:

mysql> select @@datadir;
+----------------------------------------------------------------+
| @@datadir                                                      |
+----------------------------------------------------------------+
| D:\Documents and Settings\b394382\My Documents\MySQL_5_1\data\ |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

Thanks Barry Galbraith from the MySql Forum http://forums.mysql.com/read.php?10,379153,379167#msg-379167

WAMP stores the db data under WAMP\bin\mysql\mysql(version)\data. Where the WAMP folder itself is depends on where you installed it to (on xp, I believe it is directly in the main drive, for example c:\WAMP\...

If you deleted that folder, or if the uninstall deleted that folder, if you did not do a DB backup before the uninstall, you may be out of luck.

If you did do a backup though phpmyadmin, then login, and click the import tab, and browse to the backup file.