Are you using LR 4?
As bhop noted, it does sound like a color space issue.
Hmm... That could be possible.
e.rose, I was indeed talking about a blank layer in which you apply the image.
If this does not help the color space might actually be a good thing to look at.
Just check the Image>Mode menu to see what it is at (RGB, CMYK, LAB, etc). If it's not at RGB try setting it to RGB and see if that changes the image in the same way... If so: There's your problem.
Ps. You can upload psd files to file upload sites, not sure which ones are popular nowadays but there should be loads of them around (I think mediafire is one?). Uploading a public file to dropbox would work too.
What I meant is maybe lightroom is set for rgb and psd is set for cmyk (for example) and when you're importing the file it's converting it and making it wacky.. just a thought, maybe not..
Oh? Would you please elaborate on that? Are you referring to Lightroom's Develop module?
Perhaps the issue is Lightroom 4 and CS 5 use different Process Versions of ACR, though LR 4 can be configured to use the same PV that CS 5 uses.
LR 4 - PV 2012 - ACR 7
CS 5 - PV 2010 - ACR 6