lost windows in System Preference/Start Up

IMAC 27" one year old with LION. Had WIN 7 installed with Bootcamp and worked for months OK.
Now no longer shows Windows disk in options when I go to System Preferences, Start Up Disk - it just disappeared.

Can use the Option button on a USB keyboard when powering on to select
Windows 7 but the wireless keyboard (aluminum) will not do it.
Hate to have to use a separate USB keyboard to get into Windows when
it used to work just fine using the selection in Start-up disk for rebooting
in Windows.

How can I get the Windows disk back into the Start up options?

Any suggestions? Thanks.

This can be tricky - I ran into myself once with a certain version of Paragon's NTFS for Mac. Did you happen to install any third party NTFS drivers?

For a quick and simple fix, try QuickBoot.

Quickboot also does not show the Windows disk partition

thanks for your tip - I downloaded and installed Quickboot but the result is
unfortunately the same: The Windows disk partition is not visible in the
choice of drives to boot from. Thus I can reboot the MAC LION disk with
it but still can't get to WIN7.

Very frustrating - if at least the bluetooth keyboard would work with the Option key then I would not need two keyboards on the desk.

The next time you boot the machine in Windows, run a CHKDSK on it.

Using Windows 7, how do I run CHKDSK? - Microsoft Answers

ran chkdsk but no change

there were no errors on the drive. however it still does not show up in
boot camp selection.