So I recently bought a new work computer. I've been transferring all my programs and files over to the new one and it's been a fairly laborious process.

Currently I seem to have everything working save for one crucial element: I cannot import any video files into Sonar.

What happens is if I import a video file, I get the error message "Unable to Import Video, unrecognized video format." I get this message with every type of video format including video files that worked in Sonar on my old computer. Strangely, following one failed attempt to import a video file, whichever session I failed to import the video with can no longer even attempt to import a video. The "Import Video" feature is not grayed out in the file menu, but after the initial failed attempt clicking "Import Video" no longer even brings up the dialog box giving me the option to import videos. Furthermore, if I save that project, close it and attempt to reopen it, Sonar becomes stuck about 3/4s of the way through opening it and I am locked out of that project from then on.

I've been trying to get cakewalk tech support to help me with this, but they no longer have phone support and they are very lackadaisical in responding via email. I know I have a film score project coming up in the next week or so, so I'd like to get this issue sorted out by then.

Does anybody know what is going wrong? 

Hi, and welcome to this forum.
Have you tried different video formats? 
IIRC, AVI and MP4 are preferred video formats to use.
Others will know far more about it.
All the best.

Thanks for the welcome and thank you for your reply!
I have tried a bunch of different video formats, including .avi and .mp4. None of them seems to be working at all.

The weirdest part is that on my old computer, with the same instance of sonar, many of the video files that *aren't* working now were working just fine. I don't remember having any issues on my old computer with sonar not importing video files.

Did you install any codecs on your old pc?
Could be worth checking, if possible.

https://www.codecguide.com/about_kl.htm
Careful where you click though - you just want the codec pack, not the other junk that is all to easy to download inadvertently. Usually the "standard" pack is what you want.

I may have installed codecs on my old computer, though it would have been in addition to something else like adobe premiere or something. I no longer have premiere (I used to work for a company who paid for premiere, but when I went freelance, that expense seemed a bit exorbitant)

So I'm gonna try that standard pack you suggested. 

Thanks guys, I'll report back to see if it worked.

So I installed the standard pack, but I'm still receiving the error message "Unable to Import Video, unrecognized video format." And after the first attempt at importing a video, the sessions still lock me out if I save, close and reopen them.

Aaaagh, this is so aggravating. What else should I try?

Can you play a video that you can't get to work in SONAR in Windows Media Player?
 

Is it possible that the audio bit/sample rate of the video is causing the problem?  Does it match the Sonar setting?

Well, I don't have windows media player—it apparently doesn't come native on the version of Windows 10 I have (Windows 10 N), but I'm working on getting it. It's kinda been a hassle trying to find the install file on Microsoft's website (It says I need to install the Windows Feature Pack to get Windows Media Player, but when I install it, Windows Media Player doesn't install) 
Does anyone happen to have a link to get Windows Media Player for Windows 10?

However, all of these files work in VLC player and most work in Quicktime. It does seem that it's something in Sonar that is preventing it from working.

I'm gonna check to see if the bit rate may have something to do with it. Just a second.