Airport connectivity problem

[Christina99]

I have a problem with airport connectivity.
I have a 500GB Time Capsule, an imac and a g4 laptop, working wirelessly with the time capsule.
The laptop has no problems, but the imac has slow-downs in throughput and sporadic signal loss. Sometimes very slow internet connectivity.
When using ftp the ftp program gives me prompts: "Could not retrieve file listing" "Couldn't establish data connection"
It's weird because in the airport configuration program everything seems to work fine and there is no problem.
I must say I remember a while ago I changed some settings in preferences, but I can't remember what exactly, and I tried everything, also settings in my firewall.
Any ideas?

 

[alphaod]

Okay, lets start by undoing what you did to your firewall—what did you do exactly?

 

[Christina99]

I activated 'stealth mode', but I de-activated it, and still the same problems.
I must have done something else as well, but can't remember