Black Screen during Win7 install.

I'm installing Windows 7 on this Dell laptop, which has no DVD drive, by a USB key.
Problem:
1. BIOS loaded with optimal defaults.
2. Set USB key at first.
3. Starting windows logo appears.
4. BLACK screen with mouse. Mouse moves BTW.
Specs:
2GB ram, 250GB HDD set to AHCI mode.
I tried all the possible fixes listed on the web but nothing works.
Also, there's no windows 7 already installed in it so please don't suggest DISKPART commands because I don't get that screen where I'd shift+F10.
Tried to boot Ubuntu but it gives some error after that the logo appears and keeps on going.

Try ide instead and change usb ports

Please edit your profile with all hardware details so we can read them.
AHCI mode is correct.
I would say that your Win 7 installation USB flash disk is the problem.
Did you try to boot it on another computer?
How did you made the Win 7 installation USB flash disk?
USB Windows 7 Installation Key Drive - Create

Please do specify the laptop model.

As if it old model, it may not boot properly on USB flash drive.
Currently all or mostly all, computer come with 4 GB RAM. 2 GB RAM is almost absolute.

Go to BIOS and check if it recognize the USB SanDisk model name, and HDD,say, Seagate 250 GB with model name.

Also, if no Windows 7, then is there any other OS were already installed.

I do hope your comp has got USB2 ports.

Roy

First of all, thanks to all of you for replying here.
Yes, i tried with ATA mode, which is I guess IDE, but default is AHCI.
My USB key is working fine because I do it on a daily basis. I run a computer maintenance business.
It's Dell Inspiron P071. It's my customer's laptop BTW. And yes it recognizes my USB key with it's name. I tried live booting with Ubuntu. I usually use it to check the health of HDD, getting files for backup and all that geeky stuff. Doesn't really work.
Yes yes it has USB 2.0 ports.

My conclusion is the ram. I think it's damaged.

Apart from this hardware malfunction, can this error occur by some other issues not related to hardware?
I'd like to know that.
Tomorrow after getting a new ram stick i'll check if the installation works for me. And so will report back here.

I'd like to know more about this error. Please do share if anything remotely related to this problem may occur while i'm working.
Thanks :)

Before you buy a memory stick, do a memory diagnostic test (%windir%\system32\MdSched.exe).