I know the best bet in this situation is for the testers to go through the process of reporting blocking-type problems initially show up, with the focus being on critical bugs. Since, this type of problem can high severely affect on schedules and indicates deeper problems in the software development process.
This situation will occur due to insufficient unit testing or insufficient integration testing, poor design, improper build or release procedures, etc. These are the major reasons.
What are the other steps which we have to follow as a QA if the software is so buggy?