Rancilio Silva - coffee lost its punch

Try backwashing the group with purocaff.
Are you using coffee ground at the store or do you grind just before use?
How fresh is the coffee less than a month or more?
If more than a month(whole beans) it is no longer useful.
If more than a 3 days(ground), that is stale also. It will be very diffucult to get good espresso from that(not impossible, but difficult).

If using store ground, it cannot be ground older than a week(coffee loses flavor and taste minutes after being ground). Try getting less coffee more often and adjust the grind setting that you use. If you have always used setting 3 on the store grinder try 2.5.
If grinding at home adjust the settings on the grinder to a slightly coarser grind and fill the portafilter slightly over the top of the basket, now tamp to the indent(fill line) in the basket. that should be sufficient to pull a great shot.