Inzwischen habe ich die Lösung für dieses Problem selber gefunden.
Für alle die es interessiert, hier die Anleitung von Cisco:
Reloading the Access Point Image
If your access point has a firmware failure, you must reload the complete access point image file using the Web browser interface or on 1100 and 1200 series access points, by pressing and holding the MODE button for around 30 seconds. You can use the browser interface if the access point firmware is still fully operational and you want to upgrade the firmware image. However, you can use the MODE button when the access point has a corrupt firmware image. On 350 series access points, you cannot use the MODE button to reload the image file, but you can use the CLI through a Telnet or console port connection.
Using the MODE button
You can use the MODE button on 1100 and 1200 series access points to reload the access point image file from an active Trivial File Transfer Protocol (TFTP) server on your network or on a PC connected to the access point Ethernet port.
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Note You cannot use the mode button to reload the image file on 350 series access points. To reload the image file on 350 series access points, follow the instructions in the "Using the CLI" section.
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Note If your access point experiences a firmware failure or a corrupt firmware image, indicated by three red LED indicators, you must reload the image from a connected TFTP server.
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Note This process resets all configuration settings to factory defaults, including passwords, WEP keys, the access point IP address, and SSIDs.
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Follow these steps to reload the access point image file:
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Step 1 The PC you intend to use must be configured with a static IP address in the range of 10.0.0.2 to 10.0.0.30.
Step 2 Make sure that the PC contains the access point image file (such as c1100-k9w7-tar.122-15.JA.tar for an 1100 series access point or c1200-k9w7-tar.122-15.JA.tar for a 1200 series access point) in the TFTP server folder and that the TFTP server is activated. For additional information, refer to the "Obtaining the Access Point Image File" and "Obtaining TFTP Server Software" sections.
Step 3 Rename the access point image file in the TFTP server folder to c1100-k9w7-tar.default for an 1100 series access point or c1200-k9w7-tar.default for a 1200 series access point.
Step 4 Connect the PC to the access point using a Category 5 (CAT5) Ethernet cable.
Step 5 Disconnect power (the power jack for external power or the Ethernet cable for in-line power) from the access point.
Step 6 Press and hold the MODE button while you reconnect power to the access point.
Step 7 Hold the MODE button until the status LED turns red (approximately 20 to 30 seconds), and release the MODE button.
Step 8 Wait until the access point reboots as indicated by all LEDs turning green followed by the Status LED blinking green.
Step 9 After the access point reboots, you must reconfigure the access point by using the Web-browser interface or the CLI.
Gruß
Goretex