problems running and connecting to Oracle

I'm trying to install and run Oracle on my standalone PC.

I've installed it, and created a database.  I try to connect in DBAStudio using SYSTEM/manager or SYS/change_on_install but I'm having problems.

first, the listener keeps crashing. I get the message TNS:no listener. I restart the listener with ' lsnrctl start ' then a few minutes later an alert box pops up telling me :

TNSListener error
problem writing instruction (---------) to addresss (--------) the memory could not be read.
Press OK to terminate the program.

Any idea why this is happening?

Even when the listener is running I can't connect. When I try I get the error TNS:packet writer failure.

according to this troubleshhoter guide, its a network error, but I'm on a standalone PC.
http://www.cryer.co.uk/brian/oracle/ORA12571.htm

I've also changed the sqlnet.ora as suggested, no joy there.

Any ideas, Oracle experts?

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