It worked fine yesterday, but when I click on a world to open it it crashes, here is the crash report:
EDIT: I can join multiplayer servers without error
---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.

Time: 3/23/14 4:55 PM
Description: Rendering screen

java.lang.RuntimeException: Failed to check session lock, aborting
at bdp.h(SourceFile:48)
at bdp.<init>(SourceFile:34)
at bdl.<init>(SourceFile:15)
at bdm.a(SourceFile:70)
at bfr.a(SourceFile:1688)
at bja.e(SourceFile:165)
at bjb.a(SourceFile:217)
at bhs.a(SourceFile:189)
at bja.a(SourceFile:190)
at btf.b(SourceFile:975)
at bfr.ai(SourceFile:828)
at bfr.f(SourceFile:755)
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 bdp.h(SourceFile:48)
at bdp.<init>(SourceFile:34)
at bdl.<init>(SourceFile:15)
at bdm.a(SourceFile:70)
at bfr.a(SourceFile:1688)
at bja.e(SourceFile:165)
at bjb.a(SourceFile:217)
at bhs.a(SourceFile:189)
at bja.a(SourceFile:190)

– Screen render details –
Details:
Screen name: bjk
Mouse location: Scaled: (196, 125). Absolute: (393, 229)
Screen size: Scaled: (427, 240). Absolute: (854, 480). Scale factor of 2
Stacktrace:
at btf.b(SourceFile:975)
at bfr.ai(SourceFile:828)
at bfr.f(SourceFile:755)
at net.minecraft.client.main.Main.main(SourceFile:121)

– System Details –
Details:
Minecraft Version: 14w11b
Operating System: Windows Vista (x86) version 6.0
Java Version: 1.7.0_21, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
Memory: 55585144 bytes (53 MB) / 95191040 bytes (90 MB) up to 518979584 bytes (494 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 14w11b
LWJGL: 2.9.1
OpenGL: Intel 915G GL version 1.4.0 - Build 7.14.10.4764, Intel
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Not using framebuffer objects because OpenGL 1.4 is not supported, EXT_blend_func_separate is supported, OpenGL 3.0 is not supported, ARB_framebuffer_object is not supported, and EXT_framebuffer_object is not supported.
Anisotropic filtering is supported and maximum anisotropy is 4.
Shaders are not available because OpenGL 2.1 is not supported, ARB_shader_objects is not supported, ARB_vertex_shader is not supported, and ARB_fragment_shader is not supported.

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