Thank you for your post, I am sorry to hear that you are experiencing problems.
In the Picoscope software what voltage range is specified? Try manually selecting the ±20V range and see if this helps.
Have you specified that you are using a X10 probe in the software? You can do this by going to Settings | Probes and selecting the probe you are using on the channel.
If this is still producing problems, then please email us a .psd file showing the signal that you are seeing, and explain the problem and the various things you have tried. The address to email it to is:
Hope this helps