I have just installed 9i personal on XP and had everything running fine. I.e able to create schemas, users, access SQL Plus use Oracle Enterprise Manager - everything.
I then installed 9i Developer Suite - now when I try and use any product except for SQL Plus, I get TNSListner problems. Usual error message is Cannot find it - Timing out problems. Even when I try and reconfigure the Listner using Oracle Net Configuration I get Time Out problem.
First check your environment and make sure that everything is setup correctly path etc. Second check the registry and see if the Oracle hive has been corrupted. You might be able to compare it to another machine if you have Personal Oracle installed elsewhere. Finally post your listener.ora, sqlnet.ora and tnsnames.ora files. As well as go to lsnrctl do a status and post that. It could be any number of things. But without a clear error message and the above files it is hard to tell.