Fix 0xC0000005 application crash error?

Almost all my installed programs (Firefox, skype, other 3rd party programs, ...) crash. They all assigned with EventID:1000 and Exception code: 0xc0000005.

I have tried to change the memory but that did not help.

I think it might be virus or malware. How I can fix this error?

You can test the memory by booting a liveCD (or from an USB pendrive). If that OS and its programs work well then it is not hardware related.

If an other OS also crashes (without you trying to open files in the original possibly infected HDD) then it is a hardware problem. Memory hardware problems can be the RAM, but also the memory controller, the CPU, the chipset, the traces on the motherboard etc etc. Thus just changing the RAM is a good first test but not guaranteed to solve the problem.

Instead: try these things:

1. Another OS to see if it is software related (Live CD, format and reinstall. A different HD in the PC and booting from that, ... almost limitless options).
2. If it is not the hardware scan for malware. See this post.
3. If it is neither, then carefully remove as much as possible from the PC and check if the problem goes away (e.g. use a single DIMM, try multiple memory slots. Check everything is properly seating into slots and sockets. Remove extra sound cards, additional NICs etc etc.).