Whay error code 0xc0000005 ocure whel i open facebook in wnxp

The error 0xC0000005 is generated by an illegal "memory access violation". This can be caused by anything from faulty RAM, an incorrect/corrupt device driver, poorly written/updated software and more commonly under Windows XP Service pack 2, malware/adware installations.

Usually you get this error message when performing a specific task, and if that happens you need to check the corresponding 3rd party's website/support department to see if they are aware of the problem

..a while back Symantec Antivirus caused the 0xC0000005 error with an additional message about a file called SAVRT.SYS . A simple software update to the Symantec Antivirus cured the problem.

So what can you do...? well below are a couple of suggestions:
In Windows XP Service Pack 2 Microsoft introduced Data execution prevention (DEP), a set of hardware
and software technologies that perform additional checks on memory to help protect against malicious code exploits. In Windows XP SP2, DEP is enforced by both hardware and software.

Some software/application behaviours are incompatible with DEP - data execution prevention. Applications
which perform dynamic code generation (such as Just-In-Time code generation) and that do not explicitly mark generated code with Execute permission might have compatibility issues with data execution prevention. Applications which are not built with SafeSEH must have their exception handlers located in executable memory regions.

Applications that attempt to violate DEP will receive an exception with status code STATUS_ACCESS_VIOLATION (0xC0000005).

If an application requires executable memory, it must explicitly set this attribute on the appropriate memory by specifying PAGE_EXECUTE, PAGE_EXECUTE_READ, PAGE_EXECUTE_READWRITE or PAGE_EXECUTE_WRITECOPY in the memory protection argument of the Virtual* memory allocation functions.

If you are having issues with 0xC0000005 errors in DEP and a particular piece of software is causing the offense, contact the vendor for a resolution...

Note: It is possible to "Turn Off" DEP in the boot.ini file but this really would be a last step!