I accidently deleted system cache from my xbox, can I get it back somehow and if not will it mess up my xbox..

I would like you to power cycle your network equipment, once more, as suggested up front and, also, clear the Xbox system cache 3 times in a row. Here we go!
Power off your network equipment (modem and router) for 5 minutes. Power on the modem and wait one minute for it to connect properly. Power on the router and wait another minute. Power on the Xbox and go to Xbox network settings. Select Configure Network and slide to the Additional Settings tab. Select Restore network settings to factory defaults. If wireless, reconfigure Xbox wireless settings. If wired, Press "B" on your controller and select Test Xbox LIVE Connection.

Clear Xbox system cache

1. Press the Guide button on your controller, go to Settings, and select System Settings.
2. Select Storage or Memory.
3. Highlight any storage device, and then press Y on your controller.
4. Select Clear System Cache.
5. Clear your Xbox system cache 3 times in row.

Restart your console.

Try download your profile from LIVE.

There seems to be several people online having the same problem, with no real solution in sight, so unfortunately you may have to wait for Microsoft to recognize and patch the problem. However, in the meantime some people seem to have had success by clearing their Xbox's cache, which will delete all the temporary files on your system used for game updates. This should not delete any of your game files, though it will remove saved pictures of your friends. This walkthrough on clearing the cache is from Microsoft (http://support.xbox.com/en-us/pages/xbox-360/troubleshoot/hardware/clear-system-cache.aspx):

To clear the system cache

1. Go to My Xbox, and then select System Settings.
2. Select Memory.
   
   
   
3. Highlight any storage device, and then press Y on your controller.
   
   
   (It doesn't matter which storage device you select; the cache will be cleared for all storage devices.)
4. Select Clear System Cache.
   
   
   
5. When prompted to confirm storage device maintenance, select Yes:

common problem your disk drive is messed up and u need to clear cache to do this go to system settings them memory then hover over your hard drive click y then click clear cache if this does not work contact xbox at 1-800-4my-xbox

your disk drive is messed up try taking disk out then shoving the tray back in fast then the lazier will reset if that doesn't work go to system settings then go to memory hover over your hard drive click y then clear system cache if thay doesent work contact xbox at 1-800-4my-xbox

your xbox 360 disk drive is messed up and you need to clear cache to do this go to system settings then memory then hover over your hard drive and clic ky then click clear system cache if this does not work contact xbox at 1-800-4my-xbox

your disk drive is messed up and you need to clear the cache to do this go to system settings them memory then hover over your hard drive then click y then clear system cache if that doesent work contact xbox at 1-800-4my-xbox

your disk drive is messed up you must clear cache to do this go to system settings then memory then hover over your hard drive then click y then clear system cache if this doesent work contact xbox at 1-800-4my-xbox

Try the following:

1. Hold disc by the edges without touching the surface with your fingers. Clean the disc with a soft cloth, lightly wiping from the center outwards. Do not use solvents or chemicals to clean the disc. Examine the disc for any visible signs of damage.
2. Verify whether the Xbox console clock is set correctly.
   • Turn on the Xbox console without a disc in the drive.
   • Press the directional pad up or down to select Main Menu, and then press A.
   • Press the directional pad up or down to select Settings, and then press A.
   • Press the directional pad up or down to select Clock, and then press A.
   You can see the date and time from this screen. Correct the date and time as neccessary.
   
   
3. Try to play the game again. If this does not work, you can try to clear the game cache on the Xbox hard disk. If you have a Xbox Memory Unit available, copy the game cache for this game from the Xbox hard disk to a memory unit:
   1. Insert a memory unit into a controller connected to your Xbox console.
   2. Open the disc tray and remove any disc, if present.
   3. Close the disc tray and re-start your Xbox console.
   4. Select Memory from the main Xbox Dashboard, and then press the A button.
   5. Select Xbox Hard Disk, and then press the A button.
   6. Locate and select the game you want to back up in the list of games.
   7. Select the appropriate save game icon. The Save game icons are located to the right of the game icon. Each save game is identified with a name, date, time, and size.
   8. Press the A button to display the Copy/Delete menu for the save game.
      
      Note: If Copy is not available, you have not chosen a save game file.
   9. Select Save, and then press the A button.
   10. Press the A button again to save to the appropriate memory unit.
   11. As soon as the copy is complete, press the B button to return to the list of save games.
   12. Repeat these steps as needed to back up your other saved games for this game.
   If you do not have a memory unit, deleting the game cache removes your progress in the game, high scores, and other information. To find the game cache, follow these steps:
   1. Open the disc tray and remove the any disk, if present.
   2. Close the disc tray and re-start your Xbox console.
   3. Select the Memory option from the Dashboard.
   4. Select the Xbox Hard Disk.
   5. Locate and select the game in the list of games.
4. Select the large game icon to the left of the list and press the A button.
5. Press the Abutton again to delete the game cache file.
   Note: Delete should be the only available option. If Copy is available, you have chosen a game save file and not the game cache file. Press the B button to return to the list, and then select the leftmost icon.
6. Select Yes to permanently delete the game cache, and then press the A button.
7. Confirm that the icon is no longer listed, and then re-start your Xbox console.
8. Insert the game disc, and then either load your latest saved game from the memory unit, or play the game from the beginning.

This is often caused by a damaged/dirty disk or corrupted downloaded maps.

First, clean your game disk. Then I would suggest cleaning your consoles lens with a cd cleaner or can of compressed air.

Next I would copy your game directly to your consoles hard drive. Go into your game library and you will see the option when you navigate to halo3.

If it is a downloaded map that will not load:
Delete the map from your hard drive and redownload it from marketplace. If you are using the same gamertag that you originally downloaded the map with, then this should be a free download.

You can also clear your 360's cache. Instructions for this process are below. After clearing cache, you will have to download updates for any game before playing.
http://news.teamxbox.com/xbox/11131/Xbox-360-Cache-Clear-Code-Revealed/

OK, I think I can slove your problem.

There is a slide setting thing on your av cord that gives you the option of using TV or HDTV (look near the end of the cord that slides into the XBOX 360), You will see two choices for settings on the cord "TV" or "HDTV".
Just make sure that you have it on the correct setting. I had the smae problem. My XBOX 360 is not hooked up to HDTV, so for me it should stay on TV. But somehow when I took out the cord I accidently slide it to HDTV.

I simply slide it back to the "TV" Setting and in about 30 seconds it worked perfectly.

I hope this helps you.