Microsoft is currently investigating a number of issues where Windows Phone 7 owners claim their devices have been left in an unusable state after a recent platform update.
The software giant said on Tuesday that it is “aware” of the issues and is “looking into” recent reports of “bricked” devices. The issues stem from a Windows Phone 7 operating system update issued on Monday. The update, more of a patch, was ironically pushed to improve the platform update process. Microsoft is preparing to issue its first major platform update, codenamed “NoDo”, in early March.
A number of Windows Phone 7 users applied the patch on Monday and some Samsung Omnia owners devices have been left in a “bricked” state. Devices simply instruct users to connect them to a PC, hard resetting the device or connecting it to a PC does not appear to solve the issue.
Microsoft’s Windows Phone 7 support team is recommending users return their phones to stores to get them exchanged:

Microsoft's recommendation for broken WP7 devices
There’s an ongoing thread on Microsoft’s support forums regarding these issues and one support personnel says that the software giant may re-issue the update in 3 days time:
We would recommend at this time, not to retry the update, as subsequent attempts will fail similarly. While we continue to investigate the issue, we would ask that you not attempt the update until your device alerts you of another update opportunity, in approximately 3 days’ time.
WinRumors is currently awaiting a further statement from Microsoft’s PR team.

Windows Phone 7 update - Connect to PC