You will get that type of error message if the system is looking at the wrong drive to boot. If you were have changed the drive order in the bios, or had a bootable flash drive, or some other change in drive configuration, you might see that message. Having worked on your DVD drive, the bios boot options may have been changed. Are you running a second hard drive along with the SSD?
Also, if for some reason, the boot files had become corrupted, something along that line might show up.
To run these commands, you need to boot to the Windows 7 install DVD, or the Recovery CD. After you do that, you can try a startup repair, which is probably what the link Trouble provided explains. That is supposed to run several of the recovery utilities and attempt a repair, but doesn't always work. If it does not work, and it may take 3 attempts with reboots in between, you can try opening a command prompt and use the commands below.
Other commands you can try from the command prompt are:
bootrec /scanos
bootrec /rebuildbcd
bcdboot C:\Windows
These commands may be able to replace something corrupted in the boot files. The bcdboot command, which replaces the BCD store with a new one, may be your best bet. But make sure and check the boot order in the bios.
