Wolfam your symptoms are exactly as I described in post. What is happening when your signal waves to lets say 29-30 SNR your modem gets signal strong enough to start connecting procedure. So its starting but then signal drops again to 22 SNR so it could not finish it and is flashing. Sometimes it is lucky it starts and finish but it gets disconnect after.
Do few simply things:
(FIRST)
1. Go to START>RUN type: cmd
2. In command prompt type: tracert/? - it will pop up trace route help menu.
3. Then try to trace route to lets say
Yahoo! type: tracert
Yahoo!
4. First thing on list is your NTL gateway, tru this u connect WWW.
Their gateway in Ireland is called: ntlworld.ie
5. Type ping/? - it will pop up ping facility help menu.
6. Then ping your gateway,lets say 100 times, type: ping ntlworld.ie -n 100
7. Read raports
On wired connections usually the are no losses on ping every ping is answered - 1-2% of losses are rare but possible pinging very remote location like server in located in Maledives. Wireless is different more depending from on weather - general rule is if u got more then 10% of losses on ping your connection speed will be visibly affected asking again for lost packages.
(TWO)
1. Connect your PC directly your NTL modem.
2. Go START>CONTROL PANEL run Network Connections.
3. In Network Connections click on your connection and in first bookmark thick - Show Icon in Notification Area.
4. On icon in Notification Area next to your system clock - right click take - STATUS.
5. Then click on bookmark called Service - you looking for Default Gateway.
6. Open browser u using Firefox/Opera/IE in address field type your Default Gateway address lets say: 192.168.1.1
7. It will open your modem website or pop up ask for pass and log to it.
8. Try default popular configurations like: log: admin or root / pass: admin or root.
9. If it wont work see your modem - type it serial number or name to Google and look for manual on producer site.
10. In your modem go to Downstream.
Results: Signal power is not very important thing here it can be from -15 to +36 dBmV. More important is signal SNR - Signal to Noise Ratio.
In shortcut u can have very powerful signal but full of noise ( no connection ) and u can have very week signal with zero noise ( good connection ).
Your signal SNR should be stable and minimum 34 to make your net working anything below that will coz huge loss on ping or disconnections.
SNR should int reel should be stable.
Have a Fun