You're most likely looking at one or a combination of these issues:
- Coffee ground too fine
- Coffee tamped too hard in the basket
- Brew screen clogged
- Portafilter clogged
Does water flow through easily with the portafilter removed from the machine? Then your screen is probably fine. Does water flow through the portafilter easily when there's no coffee in it? Then your portafilter is probably ok. You're then looking at a grind/tamp issue, not a problem with your machine.