When I turn my computer on, I get a loud alarm

As the computer is turning on, keep pressing the f8 button until a menu appears. Select the "safe mode with command prompt"

when it has finished loading type this
net user (user name here) (new password here)
fill the information in brackets yourself as I don't know this info.
e.g. to change a password on an account called "admin" to "open" I'd write this.
net user admin open

IOBit.com has driver booster that will scan, identify, download, and install drivers. There's a free version and a paid version. This is assuming you're using Windows 7 or higher.

Hi laptop jacki...
Go to the following website and download your FREE user manual.
Please take time to rate me

http://manualfile.net/acer-aspire-one-d250-user-manual.html

press and hold Fn key and NumLK key (blue keys) then release number lock

Hello what model is your acer, you just pointed out it was an acer aspire one net book theres different models, however your best bet is when you do find out what model your acer aspire one is, go to google type in your model number then the webcam driver and the operating system which is windows 7, for example: acer aspire one netbook zg5 windows 7 webcam driver.
If your stuck just add what model number your acer aspire one net book is and i will be happy to help you out.

you should perform a battery refresh, this will recalibrate the power meter.

if this is a wireless mouse then the usb connecter and the mouse both need to be synched up to each other. there is usually a small button on them both.

Here are a few things to try.
If you are using Windows XP Service Pack 2, refer to this Microsoft Article http://support.microsoft.com/kb/892896.
Try powering off your router for 30 seconds or so and turing it back on and try to reconnect.
Check to see if the router is giving you a IP address by running ipconfig in the command prompt. Start > Accessories > Command Prompt, and type in ipconfig. If you see an address of 169.254.x.x your router is not giving you an ip address and I would reboot your modem, computer and router at the same time.
Also could try connecting your laptop directly to your modem. If you get a connection I would contact support for the router.

your netbook is infected of virus .try to reformat

Do you see the acer splash screen before you get the black screen with the curser? If so it is more than likely a windows problem. Boot from your XP disk and select R when prompted to repair. Once in the repair console type the following:

chkdsk /r

When it is finished (will take about an hour) then type exit to restart the computer.

Hope this helps