Sieht deine Error Meldung vill. so ähnlich aus?
--- BEGIN ERROR REPORT 7fe0271 --------
Generated 21.11.10 18:50
Minecraft: Minecraft Alpha v1.2.2
OS: Windows XP (x86) version 5.1
Java: 1.6.0_22, Sun Microsystems Inc.
VM: Java HotSpot(TM) Client VM (mixed mode), Sun Microsystems Inc.
LWJGL: 2.4.2
[failed to get system properties (java.lang.NullPointerException)]
org.lwjgl.LWJGLException: Pixel format not accelerated
at org.lwjgl.opengl.WindowsPeerInfo.nChoosePixelForma t(Native Method)
at org.lwjgl.opengl.WindowsPeerInfo.choosePixelFormat (WindowsPeerInfo.java:52)
at org.lwjgl.opengl.WindowsDisplay.createWindow(Windo wsDisplay.java:185)
at org.lwjgl.opengl.Display.createWindow(Display.java :311)
at org.lwjgl.opengl.Display.create(Display.java:856)
at org.lwjgl.opengl.Display.create(Display.java:784)
at org.lwjgl.opengl.Display.create(Display.java:765)
at net.minecraft.client.Minecraft.a(SourceFile:201)
at net.minecraft.client.Minecraft.run(SourceFile:563)
at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT acde8470 ----------
Wenn ja, führ Minecraft mal aus Administrator aus (falls Vista, 7).
Dann gibt es noch eine Möglichkeit. Java updaten.