Boot problem-Partition

Hello,
I made a stupid mistake and changed my primary drive I had second thoughts but my PC automatically shut down before I could change it back. I tried to boot from a DVD disk with no luck.

I obviously have no understanding as to how the partitions in windows 7 work.

I use my computer to record music. Massive files ensued. What I did not know is that I had to route the files to the empty partition. The problem started when all of my files were saving to the system drive (c). Which is about 100 Gb. It turned red showing almost full. I saw that the 350 Gb portion was empty. I switched primary drives like an idiot. I seriously was going to change it back when my computer just shut down!!!

Now I cannot boot it. I set bios to boot from DVD but it will not. I have a guy looking at it and unfortunately he says he has to wipe the drive and cannot boot it up, stating that the 500 Gb drive is full! I don't understand this, as 350 Gb drive was empty when it shut down. I do not want to lose my files but it may be inevitable.

Can anyone here offer suggestions or explain how drives are partitioned in Windows 7 64? Is wiping the drive my only solution? I could not find any answers to this in previous posts.

Thanks in advance,

JET