Why did you restore the master database? [This is not a normal step to take in recovering a user database.]
I've got no idea what you mean by 'system data is very slow' ... ???
The mydb database was probably marked suspect as a result of your restoration of the master database (eg, you used a wrong, or old/out-of-date, master db dump file), but to know for sure would require going back through the dataserver errorlog to look for details at the point where the mydb database was marked as suspect.
As for what to do to recover your mydb database ... it's probably easiest to just follow the same instructions provided in one of your earlier threads where this same topic was discussed/resolved.