To be able to answer your question properly, we need more info:
* how many guppies did you get, and when did you get them?
* how many have died? (title mentions 'dying guppies' but content only mentions 'not swimming around')
* how many are behaving oddly / ill?
* any other symptoms?
* are there any other tank inhabitants and, if so, what?
* what size of tank is it? (in litres, plus dimensions)
* what is the brand/size of filter?
* what is your tank maintenance and filter-cleaning regime?
* what dechlorinator are you using?
* when was the tank set up?
* how was it cycled?
* what are your current levels for ammonia, nitrite and nitrates?
* what is your water hardness in GH and KH, or, from your water supplier website, what is the CaCO3 and German degrees hardness?