When the keys on the keyboard are not working properly, it is important to make sure that the keyboard is cleaned properly. Using a can of compressed air could be used to free up any dust that may be preventing the key to work. It is possible to replace the “enter” key and get a response, but it may be necessary to replace the parts under the key that it needs to function. The parts and assembly instructions can be found from a distributor of Sony products or a third-party distributor. The following link has instructions on how to troubleshoot the problem with the keyboard, and it also provides information about service options for this particular issue:
[[Sony VAIO PCG-3E2L Troubleshooting|Troubleshooting the Sony VAIO PCG-3E2L]]