ASUS EeePC 900A- black screen blinking cursor

See if you can boot to safe mode. Run check disk on the hard drive. Make sure the BIOS battery is ok.

Welcome to the world of Windows 7. Don't you miss Windows XP? LOL, Windows 7 is a nightmare just like Vista.

Anyway I think it's your Memory. You mentioned moving the memory chips around, but you didn't mention trying one at a time. I think one of them is bad.

Memory ChipRemove the Power Cord, Open the Case and remove one of thememory chips. Set the chip aside then try rebooting the computer. If it boots, then you know the memory chip you set aside is bad so mark an x onit with an ink pen. If it fails to boot then move the chip to the nextmemory slot and try rebooting. If it fails take the chip out and set itaside, then put the other chip in and try booting it in both slots. If itboots, just to verify that the chip set aside is bad, mark an x on it and putit into the open memory chip slot and try booting.Try just working with one of them in Slot 1 and swap them out in just Slot 1.

Oh, I just thought of something else, Maybe you have bad Capacitors on the motherboard. Remove the Power Cord, Remove the Case. Take a flash light and look inside the computer at the capacitors. They look like little Battery Towers. If any of them are spewing corrosion out of them, they can cause the computer to go crazy just like yours is doing.

Open On screen keyboard start - programs - accessories - accessibility - On screen keyboard
If this works then there is problem with keyboard and it needs to be replaced

if you can boot past the bios as soon as it loads up hold down f9 it will boot into a recovery partion and re-install from scratch.

According to the any brand code correct but some time code are same and problem is differ so change slot and try reboot and go to the BIOS and disable memory module single slot check it only slot me be possible memory slot is not working dot depend on dell support form only try differ

That blinking cursor is the way in which the BIOS is telling you that Windows is missing - its most critical, core files have been corrupted beyond repair. The only thing you can do is to reinstall using the recovery cd or your own Windows install disk.

corrupt boot procedure is a classic example of this symptom,Recommend re-install,restore and reboot without pressing any otherwise unwanted keys

hardware inside the laptop which amplifies may get damaged or speakers connections are open

Consider downloading a specific release of Ubuntu; eeebuntu. Download the ISO and then conenct an external DVD device to it, during the BIOS screen, choose the ESC button and boot from the external device.
This Ubuntu-specific group offers three kinds of ISO's (simple, super basic, and a loaded release), all of which allow all parts to work out of the box:
http://www.eeebuntu.org/
If this does not work, check the informal eeepc forums
http://forum.eeeuser.com/

Reboot the system
Press F8 at boot startup. In the boot menu
Choose Last Known Good Configuration. If this doesn't work

Try Safe Mode
Go to Device Manager
Roll Back any new driver you've installed
and/or
Go to Add/Remove programs
Unistall any new software you've installed