When you attempt to install a serial, or USB, modem on Windows XP SP2, you receive:

Windows was unable to install the modem.

This problem will occur if there are no Value Names under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Modem key. This condition is likely the result of removing 3rd-party modem software.

To resolve this issue:

1. Copy / Paste the following into Notepad:

REGEDIT4

\[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Modem\]
"ErrorControl"=dword:00000000
"Group"="Extended base"
"Start"=dword:00000003
"Tag"=dword:00000004
"Type"=dword:00000001

\[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Modem\Parameters\]

2. Save the file as Modem.txt.

3. Rename the Modem.txt file to Modem.reg.

4. Right-click the Modem.reg file and press Merge, or open a CMD.EXE window and type regedit /s Modem.reg.