Do you have a weth balance? the slider is in relation to your balance so it will reset to 0 if you have a 0 balance for that token.
and for limit orders, it requires one token and the price to be set. you can set the price with the plus and minus buttons next to the box
as for the scrollbars would you mind sending a screenshot of your window when they appear? And do you use mac/windows/linux and what kind of browser do you use?
we will work on improving the sliders and will most likely remove them until they are more usable. and work on improving the usability of limit orders to make them more clear.