Windows 7: Windows 7 fail to boot after ubuntu installation

Hello!
I've installed Ubuntu 11.04 on my notebook ASUS U36SD. It worked perfectly fine for 4 months.
Recently, I decided to install the last version of Ubuntu, 11.11. From now, Windows 7 doen't want to boot: It freezes at the boot screen. I tried to use the repair mode, but it failed. I also tried the safe mode. It still does't boot and freeze when loading CLASSPNP.SYS.

Please, do you have an idea about how to solve this problem?

After an installation of ubuntu, my C: partition, where Windows 7 is installed is corrupted.
From linux, I can read it and access the disk, but the windows recovery environment doen't detect it.

I think that it is because my partition is also hidden (0x17)
Do you know how to unhide this partition from linux, or to make a chkdsk on it from the recovery environment?

One easy way to repair/recover nearly any type of partition is to use testdisk on Ubuntu. You need to run it from xterm as superuser. Just follow the prompts and it should fix your problem.

Keep in mind that GRUB can corrupt Windows 7 beyond repair in almost any case, and Dual Booting is best done with Windows 7 installed last: Dual boot Ubuntu-Win7
Dual-Boot Windows 7 and Ubuntu in Perfect Harmony

That said you can try to repair Windows 7 by marking it Active then running Startup Repair - Run 3 Separate Time. Partition - Mark as Active (Method Two)

If it won't show an installation to repair, open CMD line to run: bootrec.exe /fixboot and bootrec.exe /fixmbr then see if it will show installation. If not you may have to start over and dual boot correctly.

It is always best to use EasyBCD to dual boot the two on same HD to keep GRUB off Windows 7 partition, and use separate HD's if at all possible booted only via the BIOS boot order OR one-time BIOS boot menu key.