I don't know why your computer doesn't have that option. See if your computer has the conversion program: C:\windows\ehome\wtvconverter.exe. If it does, you can run it from a command prompt window (Start >All Programs > Accessories > Command Prompt ) by typing these commands:
cd /d c:\windows\ehome wtvconverter sourcefile targetfile /ShowUI
where:
sourcefile = full path of the .wtv file that you want to convert
targetfile = full path of the .dvr-ms file that you want to create
/ShowUI (optional). If present, shows the conversion progress in a separate window
For example:
cd /d c:\windows\ehome wtvconverter "C:\users\public\public recorded tv\TV Show.wtv" "C:\users\public\public recorded tv\TV Show.dvr-ms" /ShowUI
To convert a whole folder of .wtv files to .drv-ms format, use this command:
wtvconverter sourcefolder**\*.wtv** /ShowUI
For example:
wtvconverter "C:\users\public\public recorded tv\*.wtv" /ShowUI