Teradata Express comes with a utility known as 'Teradata Service Control' usually it has a an icon on Desktop. You can use that to start/stop Teradata services.
In case it is not there, you can install it using the same Teradata Express installation.
In case it doesn't work, from windows command line (cmd) you can start Teradata service by 'net start recond'.
Make sure you have installed BYNET drivers before Teradata Database and utilities.
Yes as Adeel said, ensure your service control is up. you can check the left bottom of the service control window for the status of teradata engine. It should give a message "Teradata is running" . then only we can connect through SQL assistant (hope you are using tduser userid)
Thank you Adeel and sgarlapa for your replies. I have done everything you have suggested however I am still getting this error. One thing I noticed is the message service control showing is "PDE state is Run/Started. What should I do for it?
Some times it could be of Firewalls or antivirus installed. Can you check for a moment by deactivating them.
Some times this happens when we don't install the component in the sequence mentioned in the installatin setup.
If it corrupted more then i think good solution would be uninstall all the teradata related components through control panel and install all the components again one by one in the sequence with out miss. It worked for me earlier.