When turned on there is a dark background with vertical and horizontal stripes

1. • 1 Remove the SD card from the Garmin GPS.
     
   • 2 Insert SD card into your computer's card reader.
     
   • 3 Open the "My Computer" in either the desktop or the start button.
     
   • 4 Double click the SD card folder to open it.
     
   • 5 Hold "Ctrl" on your keyboard and left click on all the map files in the folder. Once they are all highlighted, right click and select "Copy."
     
   • 6 Go to your desktop, right click and select "Paste." You have created backup copies of the maps in your Garmin GPS. Return to the SD card folder via "My Computer."
     
   • 7 Select the map file you wish to delete, left click it once and press both "Shift" and "Delete" on your keyboard.
     
   • 8 Return the SD card into Garmin GPS. Turn it on. Check the screen to see if the right map has been deleted. If any mistakes are made, simply start over from step 1. Replace any map that has been accidentally deleted.
     
   • 
     
   • OR Insert one end of the USB cable into the USB port on the Garmin. Insert the other end of the cable into the USB port on the computer.
     
   • 2 Click on the desktop "Start" menu, and chose the "Computer" folder.
     
2. 3 Right-click on the Garmin drive folder, and select "Open." Some Garmin GPS devices (e.g., Nuvi 200 through 800 series devices) will have the map files stored here. Browse this folder for maps you want to remove, right-click on the file and select "Delete." If no map files are available, go to step 4.
   

4 Double-click to open the "Map" folder.

5 Right-click on any map file that you want to remove, and select "Delete."

try naviextras.com

Hello

Insert the memory card into the memory card slot on Garmin Nuvi 250 GPS device. The memory card slot is located on the left side of the device. Push the card in until it clicks. (If you inserted a memory card that already has pre-installed maps and files, there is no further action required. The device will access the new maps based on the address you enter.)

Connect the Garmin GPS to the computer using the USB cable. The mini-USB connector will need to be inserted into the rear of the Nuvi 250; the larger end is inserted into the computer's USB port.

Locate the computer file that you want to download to the Garmin memory card. The Nuvi 250 is capable of reading JPEG formatted images and GPX formatted Waypoints and other mapping-related files. Right-click on it. Select "Copy."

Select the "Computer" folder from the computer's desktop Start menu. Double-click on the "Removable Disk" drive that represents the Garmin Nuvi.

Right-click in an empty space within the drive and select "Paste." The files have now downloaded to the memory card and will be accessible through the Nuvi 250 menu options.

Good Luck, and do rate the solution if got help

most gps systems come with a memory card that you have to load the maps onto from a cd that is either supplied or can be purchased separately. or in some cases the memory card is pre-loaded with maps and just requires you to insert it into the memory card slot.

Nope, the data will stay there, you just insert the SD card, use the wrench symbol/select map/select about/ tick the Australia map on/the usa map off/ and you're garmin just went Aussie.

You can download the US basemap for the 500 at
http://www.megaupload.com/it/?d=EJTNQH03
Rename it BASEMAP.MGI
Then copy it in the directory "background maps" in the SD card of your 500, by using a SD card reader/writer.
Insert the SD card in your 500 and connect it to your PC; then turn it on;it will turn on regularly, because the basemap in the card will be detected; turn it to USB file transfer mode, and copy the basemap from the SD card to the directory "background maps" of the 500.

Sounds like the memory card may be inserted incorrectly or corrupt/not correct for you model.

You can download the US basemap for the 500 at
http://www.megaupload.com/it/?d=EJTNQH03
Rename it BASEMAP.MGI
Then copy it in the directory "background maps" in the SD card of your 500, by using a SD card reader/writer.
Insert the SD card in your 500 and connect it to your PC; then turn it on;it will turn on regularly, because the basemap in the card will be detected; turn it to USB file transfer mode, and copy the basemap from the SD card to the directory "background maps" of the 500.

(Untried)
For C330 owners that want to have both Canada and US 2008 map update on their GPS this is what you have to do.

Must have:
1 - Street pilot C330
2 - 512mb SD card
3 - SD card reader of some form (some cameras will suffice)
4 - Garmin 2008 Map Update North America

What to DO:

1 - connect the GPS to the computer
2 - Insert the Map update disk
3 - Install the Lower 48 states, United States
(Reason - the C330 has around 1000mb of memory and the "US 48 states" map uses around 900mb" while Canada uses 400mb...which is why you will need that 512mb SD card later)

4 - Once the GPS is updated with the US map. Browse the Map update disk contents. This can be done with going to "My Computer" right click on your CD/DVD drive and click on "Explore"

5 - Open the folder called "img"

6 - Copy the file called "gmappromU.img" file is around 430mb. (This is the map file for Canada)

7 - Insert your SD card into your card reader and connect it to your computer. A window should pop up. If not you should see it on your "My Computer"

8 - Once you have navigated your way into the SD card directory. Create a folder on the SD card named "garmin" (no caps)

9 - Go into your newly created "garmin" folder right click and paste the "gmappromU.img" file. (This may take upto 20 to 30 mins)

10 - Once the process is complete, Rename the "gmappromU.img" file to --> "gmapsupp.img" (watch for spelling, no caps at all)

11 - Remove the SD card, Turn off your GPS, Insert SD card into GPS.

12 - Turn on GPS, let it load, and there you have it, the FULL North America Map.

When you are searching a state or province (depending where you are located) it will give you an option which map to use, Canada/Alaska or the lower 48 US states. Select your map and you are set to Go.

You cannot use a sd card from another tomtom. The sd card is coded for each individual device. About the only thing you can do is to purchase a 1 gb card (no larger because it won't be supported). Insert the blank card into your unit and connect it to your pc. Go to my computer and see which drive the tt is. format the card and then open tomtom home. This will load your operating system back onto your card. I don't know if you can download a free map or not. Check the tomtom forums for more information concerning maps.
Hope this helps