Assuming you've rebooted the box once to eliminate a software issue, picture breakup is nearly always the result of signal problems. If your other box is ok, this proves the external cabling as ok so narrows your issue down to either a box issue or your internal cabling.
Package dependent, can you check the following other channels, as they share a broadcast frequency with Eurosport and would therefore prove a signal issue:
Eurosport 1HD: Shares with Discovery HD, BBC Scotland HD, Lifetime HD, Crime&Investigation HD, Sky History HD & Star Gold HD
Eurosport 2HD: Shares with Sky Sports Cricket HD, Sky Cinema Family HD, Sky Cinema Comedy HD, Cartoon Network HD, TLC-HD & Sony TV-HD
Are you able to swap your 2 boxes around, and see whether the fault follows the box or stays with the internal cabling?
If this is proved down to a box fault and a reboot doesn't resolve it, then you need to report the fault to VM. It may be an engineer visit, it maybe a box replacement.
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