Not booting up when powered on. It starts like it's going to but screen goes blue then flashing hash mark at top left of screen.

the best way restart the computer HOLD the keys CTRL or FN +f11 or f12 depend of your mark, model, and go to restore to the factory default. and restart again.
God bless you
Otherwise if the problem persis with blue screen, you must go to website computer supplier and get the suppor via ONLINE chat, for indication exactly, what goes on with your computer, you can RUN the software diagnostic coming with your computer or download from them.

2 things...
first in task manager hit "New Task" and type "explorer" and hit enter see if that brings the desktop up

2nd on boot up hit the f8 key and startup in safe mode

either way when you get to your desk top find the last good back up and do a system restore

Take the Battery out.
Place it back in.
Press and hold the Vol down : Home : Power buttons simultaneously for 10 sec.
Using the volume buttons navigate to the reset to factory settings option.
press select (left of home on L55C).
Confirm to reset.
Select to reboot.
You should be good.

Dell Suport > Dimension E510 Desktop PC > Drivers and Downloads>

http://www.dell.com/support/drivers/us/en/19

Look in the box under the Operating System subheading -
Windows Vista 32-bit.
The download page automatically opens to Vista 32-bit.

Left-click on the blue Down Arrow, to the right of the box.
In the drop down list, left-click on Windows XP.
(Works for both Home Edition, and Pro Edition)

Click on the blue Down Arrow to the left of - Audio (3)
Go down to the third file listed in blue - SIGMATEL - Driver
Go across, and left-click on - Download File

In the pop-up window make sure there is a green dot in the small circle, to the left of - For Single File Download via Browser.
If not left-click in the small circle.

Now go to the bottom of the pop-up window, and click on -
Download Now in the blue oval.
A small window will come up on the right -
Opening R114282.EXE

Left-click on Save File
Another small window will come up on the left.
In the heading at the top of the window, tells you where the file will download to.

Using Windows XP as an example;
(Doesn't matter if it's Home Edition or Pro Edition),

It may have Desktop, or My Documents, or Downloads, in the wording.

Desktop: The driver file will be on your desktop screen.
My Documents: Left-click on Start, then My Documents

Downloads: Left-click on Start, then My Documents.
DOUBLE-click on Downloads.

When you see the file name DOUBLE-click on it.
(Yes the file is OK, if a Microsoft 'Squawk Box' comes up. Click on RUN )

The Installation Wizard will appear. At the bottom of the next three small windows, click on Next, Next, and Finish.

If you are not asked to restart your computer, do so. Close all windows, go back to your desktop screen.
Restart. (Start > Turn Off Computer > Restart)

When Windows goes to load you should hear the Windows 'jingle'.

Still No?
Let the computer run for about 10 minutes or so. Surf the internet, whatever.
Now turn the computer off.
WAIT 2 minutes, turn the computer back on.

Sometimes it takes a Hard Start. { Cold Boot }
(Restart is a Soft Start. Warm Boot)

Still no? The audio chipset on the motherboard, (Integrated Audio) is bad. Suggest an economical sound card, for one of the white PCI slots.
Need guidance with this post in a Comment.

For additional questions please post in a Comment.
Regards,
joecoolvette

The monitor keeps flashing on and off? Or does your system keeps trying to reboot which causes the monitor to go on and off. Does the screen turn Blue before it goes off?

I'm not understanding what it is you are trying to say,it sounds like you are trying to describe two problems.

Projector won't flash? Are you saying nothing displays on the Screen?

And what just shows blue blink on it's power button the computer?

Blinks and Beeps tell the technician what is wrong with your system. Notice how many times it blinks and where the blinks are long or short. There is a pattern to to blinks for example (3 short blinks or 1 long blink followed by 2 short blinks).

I'm going to assume your system has a memory chip problem and when you press the power button it just blinks and nothing ever happens, not posting on the lcd screen at all.

Remove the Power Cord, Remove the Battery, Turn the laptop over and Remove the screw that secures the Memory Cover 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.

A Blue Screen is more time than not indicative of a driver issue or some hardware issue. First of all when it boots to the screen that shows Safe Mode and the other options, scroll down and see if there is an option to Stop or Disable Automatic Restart on Boot. This will stop the screen from restarting itself when the blue screen appears and give you a chance to read and see what the error is. Afterwards it is ok to run Startup Repair. Startup Repair does not delete any of your personal files. Let startup repair run and then see if it boots. Once again, startup repair does not delete any of your music, documents, pictures, videos or programs. System Restore does not delete any of you documents, music, pictures, videos or programs. System Recovery WILL DELETE all of your music, pictures, videos, documents & any programs you've added since you brought the computer home from the store. System Recovery sets your computer back to the very first time you turned it on after you purchased it. I would run the startup repair, if that does not fix your problem, see if you can run a System Restore. A lot of time the Restore Points are damaged or missing when this happens, but give it a try and restore to a point before you started having the blue screen issue. If all fails you're going to need a system disc so that you can get into the Recovery Console so that you can enter a dos command in the little black box that opens up with white letters. You want to type: chkdsk /r
Let it run. It will run well over an hour and you will notice the percentage of completion going from high to low, but that's ok. Let it run to completion then try rebooting. If this doesn't work, you're going to need to take it to a repair shop or reload the operating system yourself.

That cursor indicated that the BIOS can't find an Windows installed on the hdd. Since even the recovery partition appears to be inaccessible the only thing left is to reinstall it using the recovery cd that should have come with it when you bought it If you don't have it you can order it from Dell.

Did the HDD light flash ? also check battery may be bad, CMOS need info to talk to the drives before booting up, also is your copy of windows legal? XP and later Microsoft gives you 5 tries and windows goes bye bye, also no antivirus prog. master boot record may be corrupted. and only other thing back to O/S is linux( open source) . unles CMOS chip died.

hard disk error, insert operating system disks and run a repair or a complete clean installation.