"Available, "Can't access it" - just a cable (either direct, crossover, thru a router) is not enough.
- both computers must have IP addresses from same network (eg, 192.168.0.10 and 192.168.0.11). With direct cable connection, these settings must be set manually;
- if running Windows 7 or later - make both computer members of same HomeGroup. Otherwise - use same user name / password on both;
- a folder must be shared on "server" computer, with rights given to the account accessing it.