Reusing windows 7 oem on the same machine.

I tried manually booting the dvd drive but it still didnt work.

I bought it from amazon.
Amazon.com: Windows 7 Home Premium SP1 64bit, System Builder OEM DVD 1 Pack (New Packaging): Software

And no, i dont have any other os to test with nor another pc.
I tested the Dvd rom if it's broken it works perfectly.

Do you receive the prompt at startup to "Press any key to boot disk?"

If not the disk is not good, so burn another or try the flash stick method. Look for stick on boot menu under USB, Removable, or HD's.

Yeah i have windows7 ultimate installed in the hdd but i have no access through it coz i have forgotten the password.
And no, i didnt receive any prompt, it just goes into the loading screen.

Answering your questions.

Then how do you know the dvd drive is working fine if you can`t even log into windows ?
I booted up a norton disc, and it booted up and showed press any key to boot from dvd and it did.

I still think you`re doing something wrong, how did windows Ultimate get on this machine ? who installed it ?
I didnt install that os, my uncle did, long time ago.

And 2 other questions...

1) How do you forget a password you use every day ?
This hdd came from my sister's unused laptop, which was never used within 2years
2) Why would you setup a password in the 1st place ? (they are useless)
I didnt set up the password, my sister did, in which she forgot.
Once again:

Drop the dvd into the dvd drive, re boot the pc, tap the one time boot menu key (F10 F11 etc.) until the boot menu pops up.
Arrow down to the dvd drive then hit enter.
You should then see the words "Press any key to boot from DVD"
I already did this, it didn't work. Note that the dvd has 0 scratches and looks like brand new.

Hard to imagine Amazon would sell a bogus dvd

i would do whats posted in the link in post #5 and see about getting a refund from amazon for the disk you bought.

You said you want to reinstall Win7 Home Premium OEM you previously had on the PC. Did this laptop come with Home Premium? Is the Product Key still readable on the COA sticker on bottom? There is no reason to buy another copy of Win7 if so, since you can reinstall the licensed version of Win7 as often as you want on the same machine using that key. Everything needed to do this is provided in Clean Reinstall Windows 7. I would return the Win7 disk if you paid for any more than just a disk since you already own a license to reuse as long as the key is readable.

But you cannot expect the changed hard drive to start on different hardware. It would need adjusting but there is no need to do that since you want to reinstall anyway.

Is the hard drive detected in BIOS setup under Storage, Boot order or anywhere?

Will the disk boot without the HD which means it may be blocking the boot of the disk? If so can you put it back in your Sister's laptop to boot the disk to wipe the hard drive first with Diskpart Clean Command to clean it of boot code which may be interfering?

Otherwise download Win7 Home Premium x64 SP1 English Official ISO download to write to flash stick with Windows 7 USB-DVD Download Tool.