Hi Ish,
1. Go to command prompt ans use R3trans -d aand paste the output over here.
2. Check whether database is up or not.
3. Check whether listener is running or not.
4. Check the enc variables of your system like SAPLOCALHOST,SAPSYSTEMNAME,DBMS_TYPE etc.
5. Check the entries of the hosts and services file.
Regards,
Himanshu