Unless your dad made a backup of the encryption keys that were on his old laptop, associated with his user-Id on that machine, data in any file encrypted with those keys is now lost.
By far, the most frequent problem with EFS occurs when EFS encryption
keys and/or recovery keys aren't archived. If keys aren't backed up,
they cannot be replaced when lost. If keys cannot be used or replaced,
data can be lost. If Windows is reinstalled (perhaps as the result of
a disk crash) the keys are destroyed. If a user's profile is damaged,
then keys are destroyed. In these, or in any other cases in which keys
are damaged or lost and backup keys are unavailable, then encrypted
files cannot be decrypted. The encryption keys are bound to the user
account, and a new iteration of the operating system means new user
accounts. A new user profile means new user keys. If keys are
archived, or exported, they can be imported to a new account. If a
revocation agent for the files exists, then that account can be used
to recover the files. However, in many cases in which keys are
destroyed, both user and revocation keys are absent and there is no
backup, resulting in lost data.
File encryption uses a symmetric key, which is then itself encrypted
with the public key of a public key encryption pair. The related
private key must be available in order for the file to be decrypted.
This key pair is bound to a user identity and made available to the
user who has possession of the user ID and password. If the private
key is damaged or missing, even the user that encrypted the file
cannot decrypt it. If a recovery agent exists, then the file may be
recoverable. If key archival has been implemented, then the key may be
recovered, and the file decrypted. If not, the file may be lost. EFS
is an excellent file encryption system—there is no "back door."