Computer keeps crashing

My computer keeps on crashing and don't really know why. The computer is kind of old but is mostly used for insurance verification in my office. It runs on windows xp professional service pack three with a pentium 4 processor 2.0GHz 512MB RAM. I have enclosed the minidumps of the last three recent crashes.
 
The minidumps reveal
BAD_POOL_CALLER (c2)
BUGCHECK_STR: 0xc2_7_SAds
DEFAULT_BUCKET_ID: DRIVER_FAULT
MODULE_NAME: nt
IMAGE_NAME: ntoskrnl.exe

FAT_FILE_SYSTEM (23)
ERROR_CODE: (NTSTATUS) 0xc0000005 - The instruction at "0x%08lx" referenced memory at "0x%08lx". The memory could not be "%s".
EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at "0x%08lx" referenced memory at "0x%08lx". The memory could not be "%s".
MODULE_NAME: Fastfat
IMAGE_NAME: Fastfat.sys

KERNEL_MODE_EXCEPTION_NOT_HANDLED_M (1000008e) This is a very common bugcheck.
BUGCHECK_STR: 0x8E
PROCESS_NAME: CCSVCHST.EXE
MODULE_NAME: NAVEX15
IMAGE_NAME: NAVEX15.SYS

I would recommend...
1. Run ChkDsk (windows utility, may be run from teh command line... Start -> Run -> chkdsk
2. Get and run memtest... will require a minimum of 7 full passes, 8 tests per pass... If you start getting errors, you may as well stop, then remove your ram for testing one stick at a time. See Here ... https://www.techspot.com/vb/topic62524.html
3. Visit the Virus and Malware board, to check for infections... pay close attention to the first three notes by Julio on this page... https://www.techspot.com/vb/menu28.html
if you decide to clean, follow very carefully the instructions on this page... https://www.techspot.com/community/topics/updated-4-step-viruses-spyware-malware-removal-preliminary-instructions.58138/
if you find virus or malware infections, start a new thread there, and let us know here what you are doing.

Otherwise, we'll look for your update here.
 
Hey, sorry I couldn't answer you earlier but I am preparing for a trip. Thanks for the reply I will try to do these things as soon as I can and will keep you updated on the situation.
 
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