My IMEDIA 1559 keep asking me for an

Remove system(BIOS)battery for 5 sec,it may help sometimes.

re start your laptop then while it was rebooting the system press delete in the keyboard. the bios set up will appear then you can change the administrator password or delete then save the settings and then re start your laptop.

We can't help you in any way, to reset the pass word you need direct access to the pc.
Use this
http://pogostick.net/~pnh/ntpasswd/

How to Bypass or Remove a BIOS Password by Removing the CMOS Battery:
The simplest way to remove a BIOS password is to simply remove the CMOS battery. A computer will remember its settings and keep the time even when it is turned off and unplugged because these parts are powered by small battery inside the computer called a CMOS battery. If we pull out this battery, the computer will forget alot of its hardware settings, including its BIOS password. This should not be performed on Laptops if you are not experienced working with laptop hardware.

Log onto machine as local administrator
Launch HP ProtectTools Security Manager for Administrators
Bios Configuration -> Security
Fingerprint Reset on Reboot - Enable.
Reboot
Esc for Bios Setup
Choose Bios Option

Press F1 accept a reset of the password .

Try going to the BIOS and see if it reboots from there. If it does, then it is most probably a hardware problem. You can try re-seating the memory modules and If you have multiple modules, try them one at a time.
If it does not reboot while you are in the BIOS, then the problem lies on Windows. Get your DELL Restore CD or your Operating System CD and insert it to the CD-ROM drive. Reboot the computer and press F12 while seeing the Dell logo, that should give you the options to boot to CD-ROM. It will give you a quick prompt of "press any key to boot to cd..". Make sure you press the space bar during this time to initiate the boot from CD-ROM.
Once the Windows Setup loads, Choose "Recovery Console" to repair your computer. Just choose the installation you would like to repair (normally it's number 1) then it will ask you for the administrator password. By default, the password is blank, but if you set a password for admin then use that password.
Once you get to the prompt, Type this command. "CHKDSK /R" (without the quotes). It will initiate the repair for your OS. This might take an hour or so. Just wait for it to finish and it will automatically reboot your computer. Let the computer computer reboot normally. You should be able to get to your normal windows screen back.
Good Luck.

Are you tryingto access the bios or is this asking you when you reboot at the start up screen?

I have read many posts about the PB Imedia and problems trying to upgrade memory. Sounds like there are some motherboard issues with this PC . Some have reported success with mixing different memory types and speeds, but no real answers as to why.

You may have to check the voltage that powers the memory. Some memory sticks are rated at 1.8v , others use other voltages that will hang your system if mixed.

Check with the manufacturer for their recommendation.

If the password window has come for first time then don't enter any password. Leave the password window blank. In the user name enter Administrator and log on. If this does not help enter administrator or admin in password field. But this should be second option.

My suggestion is that you downgrade from Window Vista to Window XP as till date Windows Vista has lot of bugs relating to security issues.I myself have done that.