I'm having a issue. Lightroom cannot find these original files,

I start I'm getting the exclamation symbol on 12 photo. I can't find them anyware I look in the coresponding folder I look in the rest of the forlder from this year  and even the previous year and and even in the trash and I came out empty handed. but the rest of the photos the I took that night are ther. Let me explain; the night before I was working on especific project with those photos  I feel tired so I quit Lightroom and promt me to backup so I did. and I left my Mac to sleep mode like every other night, the only way this Mac is  shut down is when I going on a assignment the last up to 3 weeks or more. and those photos have to be the most important of this project. funny thing I can printed but I can manipulated. I use lightroom and photoshop since came out on the market no issue what so ever. The anyone had or have this issue before. cos I can think any more I can't find any solution. need a little help.