In order to help you we need more clear information.
First, you're saying customers can't pay you at all. What exactly is happening when they try to pay? What error message are they getting?
Then, you say that sometimes you do get the payment, but it's pending. Well, that's an entirely separate issue.
Payments can be pending for a number of reasons. If you click into the transaction details you should see info about this. For example, does it show that it's an e-check? If so, that would clear in a few days as long as the bank funds were available to cover the purchase.
It could also be pending because of specific flags that were raised on the transaction based on a variety of variables involved. Typically once you ship something and provide tracking that shows it's delivered, this can help release those funds.
Was it something you sold on eBay? If so, there could be a fund hold happening on their side.
Lots of directions we could go with all of this, so need more information in order to try and help.
Angell EYE - www.angelleye.com PayPal Partner and Certified Developer - Kudos are Greatly Appreciated!