As Neil said pictures would definitely help. Looking at the data sheets the BC557 should be reversed as the pinouts are the other way about to the PN4250.
The issue with the 100n is strange but they are close on the board and also to the BC557 - did you initially have the BC557 the other way round and have to desolder it? Is it possible there's been some damage to the board in that area?
Also have you tried adjusting the trimmer? I built a DUSG this week and was getting nowhere with it until I tried that - sometimes it's not a setting to taste, you need it in the right place for it to work at all.
The issue with the 100n is strange but they are close on the board and also to the BC557 - did you initially have the BC557 the other way round and have to desolder it? Is it possible there's been some damage to the board in that area?
Also have you tried adjusting the trimmer? I built a DUSG this week and was getting nowhere with it until I tried that - sometimes it's not a setting to taste, you need it in the right place for it to work at all.