Some things to try:
1) To see if Interference from the desktop is the culprit, wrap Aluminum Foil around the tuner and at least a foot along the cables going in and out of the USB Stick. And since interference can readily leak from the desktop to the antenna, use a 25 to 50-ft length of coax and temporarily relocate the antenna....preferable outside.....and see it reception improves. Open up the Alum. Foil in between tests so the USB Stick doesn't overhead. You should rewrap it each time you try the following software checks.
2) If you haven't already tried it, remove and reinstall the K-World Driver and Display Software from the supplied disk.
3) Although I would expect the installation software would automatically check (maybe it didn't?), System Requirements on K-World website for (ONLY?) the Hybrid Stick says you need a Graphics Card that supports DirectX 9.0c
and (for HD) DXVA
.....and they cite particular ATI & nVidia graphics engines....or better. Download latest software for your Graphics Card from the manufacturer's website...don't rely on Windows Update.
Info re DXVA: http://en.wikipedia.org/wiki/DirectX_Video_Acceleration
It means you need a Graphics Card that has an on-board HARDWARE ACCELERATOR which supports DXVA.
4) Download page for TiVme also says you need to have downloaded and installed Microsoft .NET Framework v3.0 or higher (check for latest version using Windows Update).
5) Using the K-World Download page, remove and reinstall Driver and TiVme software with the known good, latest versions. ALSO download and install the alternative HyperMedia Center (in beta test) program that you can try to see if it works any different:
6) You didn't say which USB Stick you have. If you have the Hybrid version, you could use the Ch3/4 output from a VCR (or other box) to see if the USB Stick is capable of processing a strong ANALOG signal....doesn't PROVE whether ATSC will work, but checks a lot of other things....
7) For either USB Stick, same test could be conducted with Clear QAM signals if you (or a friend) have Cable....and the provider hasn't killed off ALL of the Clear QAM channels (like some COMCAST systems).