Windows starts working very slowly and sometimes freezes when opening certain files

So couple of days ago I started having problems with my Win7 SP1 64bit, whenever I'm opening video files (like mkv) PC starts working very slowly (refreshing the desktop takes couple minutes, opening task manager takes even longer) and in the end I often need to force restart it. VLC player opens up, but doesn't show video nor sound. Same problem happens when trying to open mp3 and pdf files. PC works just fine until I try to open one of those files (I can play games and play videos on youtube just fine). Also in the task manager - performance tab doesn't show anything wrong and in event viewer I see critical errors just from Kernel-power when I'm restarting the PC forcefully. In errors tab these shows up: NvStreamSvc
- System
- Provider
[ Name] NvStreamSvc
- EventID 1
[ Qualifiers] 49154
Level 2
Task 0
Keywords 0x80000000000000
- TimeCreated
[ SystemTime] 2014-10-23T06:47:12.000000000Z
EventRecordID 331835
Channel Application
Computer shaulys-PC
Security
- EventData
NvStreamSvc
NvVAD endpoint registration failed [0]


WMI
- System
- Provider
[ Name] Microsoft-Windows-WMI
[ Guid] {1edeee53-0afe-4609-b846-d8c0b2075b1f}
[ EventSourceName] WinMgmt
- EventID 10
[ Qualifiers] 49152
Version 0
Level 2
Task 0
Opcode 0
Keywords 0x80000000000000
- TimeCreated
[ SystemTime] 2014-10-23T07:11:12.000000000Z
EventRecordID 331881
Correlation
- Execution
[ ProcessID] 0
[ ThreadID] 0
Channel Application
Computer shaulys-PC
Security
- EventData
//./root/CIMV2
SELECT * FROM __InstanceModificationEvent WITHIN 60 WHERE TargetInstance ISA "Win32_Processor" AND TargetInstance.LoadPercentage > 99
0x80041003


Disk
- System
- Provider
[ Name] Disk
- EventID 11
[ Qualifiers] 49156
Level 2
Task 0
Keywords 0x80000000000000
- TimeCreated
[ SystemTime] 2014-10-23T06:55:52.122208800Z
EventRecordID 118256
Channel System
Computer shaulys-PC
Security
- EventData
\Device\Harddisk1\DR1
0E04800001000000000000000B0004C003010000000000000000000000082D000000000000000000818E000000000000FFFFFFFF060000005800000000000000FF0006120C000010000000003C00000000000000000000008037F40680FAFFFF000000000000000060ACB40780FAFFFF0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

These are the three errors that I got last time this happened.

My PC specs:
Windows 7 64bit SP1
Processor- AMD Phenom II X6 1050T
Motherboard- ASRock 970 Pro3 R2.0
8Gb DDR3 RAM
GPU - Nvidia Geforce GTX 760 4Gb
PSU - Corsair VS650

I hope that's enough information to suggest what may cause the problem and sorry for my English, please excuse all silly mistakes that I make

I wonder if reinstalling windows will erase this problem, I just want to leave it as a last resort.

Thank you.