Slow network connection

Hi there, I'm running Informix Online V7.3 on Windows NT4 (sp3). In the beginning all worked fine, but after about 1 year I observed an extended delay when I connect to the server (via the native Informix driver that come with PowerBuilder 5) over the network from any client. In between, one and a half year later, I have to wait more than one minute until a network login is established. There is no delay, when I launch the client application on the db server machine. Further more, database transfers over the network are as fast as before, as soon as the connection is established. Also, there is no delay or slow down when the Windows file system is accessed from the client over the network, even while the database client is just logging in. I have had the very same problem with the preceeding installation (Informix Online V7.21). The only way I found to fix it was to reinstall the server. Thereby I didn't change any settings and also the clients stayed unchanged. Thanks for any help, Erwin