c:\boot and others corrupt

Hi! I have a strange problem. First of all i'm tired of burning dvds and at "expanding file" phase, the installation stops with the "windows could not copy the files..." bla bla, so i'm trying to install from a usb external hard drive. No problem with booting from the external drive, i can get into windows installation screens with no problem at all. but after i format the partition that i choose to install windows on, right after "copying files.." i get a message of corrupted files that can't be read, "c:\boot", "c:\boot\several files". I've tried this with windows 7 professional x64 and windows 7 professional x86. This only happens when installing from the external usb hard drive, with the dvd it usually stops at 36%... I think that it must be a problem with my destination hard drive, but i don't know... anyone can help me?
Thanks!

Hi! Yes, i always format it in the disk management setup screen before starting the setup...

Where did you get Win7? Check the ISO hash using Hashtab against official HASH here: Windows 7 RTM SHA-1 hash / checksums

Burn another DVD at 4x speed using ImgBurn, which never fails.

WIpe your HD correctly using DIskpart: SSD / HDD : Optimize for Windows Reinstallation

Make sure you have the latest BIOS update, if so reset the CMOS: Clear CMOS - 3 Ways to Clear the CMOS - Reset BIOS Set SATA controller in BIOS to AHCI first, then IDE if necc.

Remove all but 2gb of RAM to try install, test RAM with memtest86 CD for 5-6 passes.

If all this fails, test your HD using maker's diag/repair full CD scan.