Hi Logic Express,
Please can you list your Logic version, OS X version and your mac system and very importantly your audio interface.
In the meantime a few questions:
1. Was your project working before?
2. What happened that you stopped hearing audio?
3. Are your audio regions on audio tracks?
4. Are the tracks set to Output 1-2?
5. Are the level meters of the track moving or do you see and hear no audio signal coming from Logic?
6. If you switch to built-in audio (Logic Express > Preferences > Audio [Devices]
do you hear any audio?
7. Do you hear any audio if you add a software instrument track and play it?
8. Open the Mixer, are there any channels solo-ed or muted or do you see any of the M or S buttons flashing?
If none of the above work, you can switch to 44.1khz and convert the 48khz files to 44.1khz:
Open the Audio Bin and select all the audio files.
Choose Audio File > Copy/Convert audio files...
In the pop up window select 44.1 in the sample rate drop down menu and choose the file type you prefer and save.
The samples will now play back at the correct speed.
By the way, if you haven't already, check out Logic 101: Core Logic 8
It's a great tutorial that will help you understand much more abut sample rates and how to work with audio very efficiently in Logic :-)