I dont know what has happened:
crash report

---- Minecraft Crash Report ----
// There are four lights!

Time: 7/27/14 10:29 AM
Description: Handling packet

java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.addWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.execute(Unknown Source)
at java.util.concurrent.AbstractExecutorService.submit(Unknown Source)
at cjs.a(SourceFile:94)
at bzp.<init>(SourceFile:44)
at bzt.<init>(SourceFile:77)
at bvx.a(SourceFile:343)
at bjp.a(SourceFile:1849)
at bjp.a(SourceFile:1797)
at bvt.a(SourceFile:130)
at ik.a(SourceFile:72)
at ik.a(SourceFile:13)
at fq.a(SourceFile:163)
at bjp.p(SourceFile:1730)
at bjp.ai(SourceFile:839)
at bjp.f(SourceFile:793)
at net.minecraft.client.main.Main.main(SourceFile:121)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.addWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.execute(Unknown Source)
at java.util.concurrent.AbstractExecutorService.submit(Unknown Source)
at cjs.a(SourceFile:94)
at bzp.<init>(SourceFile:44)
at bzt.<init>(SourceFile:77)
at bvx.a(SourceFile:343)
at bjp.a(SourceFile:1849)
at bjp.a(SourceFile:1797)
at bvt.a(SourceFile:130)
at ik.a(SourceFile:72)
at ik.a(SourceFile:13)

– Packet information –
Details:
Packet name: ik
Packet debug: eid=70, gameType=1, hardcore=false, dimension=0, difficulty=PEACEFUL, maxplayers=8
Stacktrace:
at fq.a(SourceFile:163)

– Affected level –
Details:
Level name: MpServer
All players: 0 total; []
Chunk stats: MultiplayerChunkCache: 0, 0
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: 8.00,64.00,8.00 - World: (8,64,8), Chunk: (at 8,4,8 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 0 game time, 0 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 0 total; []
Retry entities: 0 total; []
Server brand: ~_ERROR~ NullPointerException: null
Server type: Integrated singleplayer server
Stacktrace:
at bvy.a(SourceFile:309)
at bjp.b(SourceFile:2123)
at bjp.f(SourceFile:802)
at net.minecraft.client.main.Main.main(SourceFile:121)

– System Details –
Details:
Minecraft Version: 14w20b
Operating System: Windows Vista (x86) version 6.0
Java Version: 1.7.0_60, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 1463533800 bytes (1395 MB) / 1559494656 bytes (1487 MB) up to 1559494656 bytes (1487 MB)
JVM Flags: 5 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xms1500m -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 14w20b
LWJGL: 2.9.1
OpenGL: Intel 965/963 Graphics Media Accelerator GL version 2.0.0 - Build 7.15.10.1576, Intel
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because EXT_framebuffer_object is supported.
Anisotropic filtering is supported and maximum anisotropy is 2.
Shaders are available because ARB_shader_objects, ARB_vertex_shader, and ARB_fragment_shader are supported.

Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: []
Current Language: Canadian English (Canada)
Profiler Position: N/A (disabled)
Anisotropic Filtering: Off (1)
Alocated memory: 100%