Windows 10 - Microsoft Security Client Error Code 0x80070426 - Microsoft Community

after windows 10 update installed on tuesday, 1/10/17, computer has been wreck.

1. computer extremely sluggish, gaming impossible , opening task manager takes 10 seconds. fear computer has virus.

2. wanted scan computer using windows defender, noticed windows defender not appear in icon box that's in lower right side of desktop. however, task manager says running (i found windefend under services tab). however, cannot open windows defender through update & security page. when error code above, microsoft security client error code 0x80070426.

3. have tried offline windows defender scan - didn't work.

i looked online, see solution uninstall microsoft security essentials, don't have installed according list of programs on control panel. 

i tried contacting microsoft support, in told me restore computer previous state - didn't work , got error message, telling me failed restore due no access sort of cortana file. 

i can't seem run administrator , computer fails see owner , user of computer.

here's basic information computer, please let me know if need more info.

dell xps 8100

windows 10 - upgraded windows 7 home. both geniune since bought desktop straight dell, upgraded 10 once got option to.

do not have multiple os or users

started happen after update released on 1/10/17. 

i used avast longest time until windows defender became mandatory windows 10 systems, uninstalled , started using windows defender solely. 

none of ever happened until wednesday, day after.

basically, have feeling 1 of problems these updates:

1. cumulative update windows 10 version 1607 x64-based systems (kb3213986)
2. windows malicious software removal tool windows 8, 8.1, 10 , windows server 2012, 2012 r2, 2016 x64 edition - january 2017 (kb890830)
3. security update adobe flash player windows 10 version 1607 (for x64-based systems) (kb3214628)

or it's virus somehow disabled windows defender , blocks access administrator priveleges. 

anyone got clue?

situation update: computer unusable now, way slow anything. however, did run dell diagnostics , found hard drive has problem, error code 2000-0146. might mean hard drive needs replaced, know if case? why computer seems has processing power of turnip?

fyi bios , diagnostic tools before booting works fine.

Windows / Windows 10 / Performance & system failures / PC