Check your connections to the TV - on BOTH ends - the TV & the 360. Make sure that your cables are truly connected. A cable even partly out can cause this even though it might seem tight.
If that checks out then do as the first poster suggested & remove your hard drive & play games that had been messing up. If they no longer bad then the update probably did something to mess it up. This is good as you shouldn't have to buy anything. Power off & plug your hard drive back in. Go into the setup & delete anything related to armored core 4 & then power cycle.
If that doesn't fix it then follow these steps to clear the cache (from Microsoft) it starts on step 5 (you've already completed the previous):
Clear cache steps.
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5. If the issue does not occur when the hard drive is detached, try clearing the Xbox 360 Hard Drive cache. With the Xbox 360 Hard Drive attached to the console, follow these steps:
a. Locate the System section of the Xbox 360 Dashboard.
b. Select Memory, select Hard Drive, and then press Y to view the device options screen.< BR>c. On the Xbox 360 Controller, press the X button, press the X button again, press the left bumper, press the right bumper, press the X button, and then press the X button again.
d. You will be prompted to confirm system maintenance, select Yes by pressing A.
6. If this problem occurs with the hard drive attached and clearing the cache did not resolve the issue, create a new gamer profile, and then test to see whether the issue still occurs. If the issue does not occur when you use a new gamer profile, the issue may be related to the original gamer profile or saved game information for one or more games that are associated with the original gamer profile. To verify this, delete the saved games for all games that show this problem for the original gamer profile.
Unfortunately, we do not recommend an additional cooling system. Installing this device may void your warranty and eventually will damage your console.