I didnt know where to put this crash, it told me Mojang.com, nothing else.
Crash report: ---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!

Time: 11/14/12 10:00 PM
Description: Failed to start game

java.lang.SecurityException: SHA1 digest error for pack.txt
at sun.security.util.ManifestEntryVerifier.verify(Unknown Source)
at java.util.jar.JarVerifier.processEntry(Unknown Source)
at java.util.jar.JarVerifier.update(Unknown Source)
at java.util.jar.JarVerifier$VerifierStream.read(Unknown Source)
at java.io.FilterInputStream.read(Unknown Source)
at sun.nio.cs.StreamDecoder.readBytes(Unknown Source)
at sun.nio.cs.StreamDecoder.implRead(Unknown Source)
at sun.nio.cs.StreamDecoder.read(Unknown Source)
at java.io.InputStreamReader.read(Unknown Source)
at java.io.BufferedReader.fill(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at bdx.a(SourceFile:66)
at bdx.<init>(SourceFile:37)
at bdz.<init>(SourceFile:15)
at bec.c(SourceFile:114)
at bec.<init>(SourceFile:37)
at net.minecraft.client.Minecraft.a(SourceFile:241)
at net.minecraft.client.Minecraft.run(SourceFile:515)
at java.lang.Thread.run(Unknown Source)

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

– System Details –
Details:
Minecraft Version: 1.4.4
Operating System: Windows XP (x86) version 5.1
Java Version: 1.6.0_01, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Sun Microsystems Inc.
Memory: 495168328 bytes (472 MB) / 532742144 bytes (508 MB) up to 1065484288 bytes (1016 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: RADEON XPRESS 200M Series SW TCL x86/MMX/3DNow!/SSE2 GL version 1.4.5014 WinXP Release, ATI Technologies Inc.
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: ~_ERROR~ NullPointerException: null