Windows files are lost while dual boot

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http://askubuntu.com – I have a 1TB hard disk running windows 7 on my Dell Laptop. I partitioned it into two drives one having 900 GB and the other drive having 100 GB. I installed Ubuntu alongside windows 7 and ran it successfully. The dual boot also worked for the first two times but after that when I opened my Windows drive in ubuntu it showed no files. When I rebooted and selected Windows 7 in the startup menu, then startup repair appeared and it didn't help me to gain access to my windows 7. Are my windows drive files gone? (HowTos)