Windows 7: Reinstall Windows 7, have: Win7 and Linux

Reinstall Windows 7, have: Windows 7 and Linux...

I want to reinstall Windows 7 cause there is a problem and i cant open windows 7, stops at "Welcome" Screen. Tried system repair, restore didn't work. and i want to reinstall Windows 7 over, but i boot windows 7 installation, and doesn't boot, but the screen where i choose OS comes up

Disk /dev/sda: 640.1 GB, 640135028736 bytes
255 heads, 63 sectors/track, 77825 cylinders, total 1250263728 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0f8ba9ec

Device Boot Start End Blocks Id System
/dev/sda1 * 2048 849994971 424996462 7 HPFS/NTFS/exFAT
/dev/sda2 849995774 1045465087 97734657 5 Extended
/dev/sda5 849995776 1037488127 93746176 83 Linux
/dev/sda6 1037490176 1045465087 3987456 82 Linux swap / Solaris

The screen to choose OS is a boot manager screen or a GRUB screen ?

i don't know. it was installed when i installed linux ubuntu

Look at the first line of the OS choosing screen ... Is it saying "Windows Boot Manager" or "GNU GRUB" ?

What is the OS you have installed first ? Windows or Linux ?

Grub

If you want use your existing windows installation , you follow the METHOD 2 or METHOD 3 of the tutorial Partition - Mark as Active ,to mark your windows 7 's C partition as active, and then run Startup Repair for at least three times, with restarts after every single run. Later, you can add linux boot entry using EasyBCD.

if you want to reinstall windows, follow the tutorial SSD / HDD : Optimize for Windows Reinstallation to clean the disk from GRUB and EFI partitions. But before that, dont forget to backup all your important data externally.