There are a few reasons why a vacuum may lose its suction. Here are some things to check or consider:
1. The bag may be full
2. The hose may be clogged
3. The height of the rollers isn't right for the floor surface you are cleaning
4. The vacuum/bag may not be airtight
5. There is something snagging the roller brush/beater head
Check these things first before taking your vacuum in for service. Good luck!