Game wont start

While trying to login I get a box saying MISSINGTEX then error message: Minecraft has crashed!
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Minecraft has stopped running because it encountered a problem; Failed to start game

A full error report has been saved to C:\Users\Nathan\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-04_18.51.43-client.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash

— BEGIN ERROR REPORT 7a5ed805 --------
Full report at:
C:\Users\Nathan\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-04_18.51.43-client.txt
Please show that file to Mojang, NOT just this screen!

Generated 04/01/13 18:51

– System Details –
Details:
Minecraft Version: 1.4.6
Operating System: Windows 7 (x86) version 6.1
Java Version: 1.7.0_10, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 405089312 bytes (386 MB) / 518979584 bytes (494 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 2 total; -Xms512m -Xmx1024m
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
LWJGL: 2.4.2
OpenGL: AMD Radeon HD 6530D GL version 4.2.11566 Compatibility Profile Context, ATI Technologies Inc.
Is Modded: Very likely; Jar signature invalidated
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: ~_ERROR~ NullPointerException: null

java.lang.NullPointerException
at java.io.Reader.<init>(Unknown Source)
at java.io.InputStreamReader.<init>(Unknown Source)
at bey.<init>(SourceFile:58)
at net.minecraft.client.Minecraft.a(SourceFile:322)
at asq.a(SourceFile:56)
at net.minecraft.client.Minecraft.run(SourceFile:515)
at java.lang.Thread.run(Unknown Source)
— END ERROR REPORT ad1f2ac3 ----------