windows host process has stopped working

hi,
i need help...

i have been having this problem for a quite a lot of time now..
whenever i stay connected to the internet for some time i get this
message stating that the windows host process has stopped working ..post
which none of my applications work properly... i can't even shutdown my
laptop properly i need to directly switch it off via the power off
button .
recently i have been getting the blue screen of death quite often... to
add to my problem for some unknown reason can't even open Microsoft
support sites ...
my windows defender cannot check for updates as well...
it gives an error code :0x80070422

i have already tried out the following methods to solve my problem.
1. done a memory test through the BIOS setup
2. using the cmd.exe in the admin mode did a full system scan
3. un-installed ie-8 and reverted to ie-6
4. defragemented
5. disk cleanup
6. i have no hp - printer software installed

i checked my event log and i got a application error with the following
details

Faulting application svchost.exe, version 6.0.6001.18000, time stamp
0x47918b89, faulting module ntdll.dll, version 6.0.6001.18000, time
stamp 0x4791a7a6, exception code 0xc0000005, fault offset 0x000659c3,
process id 0x4b0, application start time 0x01c9ffec5f88a4b3


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sakshi.handa