I've had my dsl 401 for about 12 years. In the United States. From the beginning, it would lose power, go silent, but then come back. Now, it has gone completely silent, won't come back, and I can't find a certified Marshall repair listed anywhere in the United States. All my searches, including on Marshall's own website, state it is for UK customers only. This issue is common with this amp. Can you point me in the right direction? I am not an engineer.