Хмм,ну я точно не знаю,но попробуйте нажать просто "Запуск". Если и так не запускается попробуйте разархивировать пример:Рабочий стол. Ибо после этих процедур не запускается, переустановите java.

"C:\Program Files\Java\jre6\bin\java.exe" -Xms564M -Xmx564M -jar Minecraft.jar
Heap size: 545.0
Heap is big size
run complite
16 achievements
Head acc: + 7
277 recipes
update not found: old c24a55a122eb21076c444e683320d345, new: c24a55a122eb21076c444e683320d345
replace complite

water_mode: 0
anti_aliasing: 2
reflection_resolution: 4
reflective_items: true
reflective_clouds: false
reflect_player: true
render_v3: 1.0
water_surface_transparency: 0.05
waterfall_transparency: 0.4
water_color: 0.0, 0.4, 0.3
waterfall_color: 1.0, 1.0, 1.0
waterfall_fog: true

WARNING: Found unknown Windows version: Windows 7
Attempting to use default windows plug-in.
Loading: net.java.games.input.DirectAndRawInputEnvironmentPlugin

Starting up SoundSystem...
Initializing LWJGL OpenAL
(The LWJGL binding of OpenAL. For more information, see http://www.lwjgl.org)
OpenAL initialized.

Connecting to 86.62.89.4, 130
H: LOL-ÏÊ, k: 8
Thead new download: cloaks/null
Try to load: cloaks/null
Thead new download: skins/Piffs
Thead new download: cloaks/Piffs
Try to load: skins/Piffs
Try to load: cloaks/Piffs
LOGIN PACKiffs
New max size: 324
New max size: 484
New max size: 784
java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Byte
at net.minecraft.src.DataWatcher.getWatchableObjectByte(DataWatcher.java:48)
at net.minecraft.entity.Entity.getEntityFlag(Entity.java:1260)
at net.minecraft.entity.Entity.isSprinting(Entity.java:1240)
at net.minecraft.entity.Entity.onEntityUpdate(Entity.java:190)
at net.minecraft.entity.EntityLiving.onEntityUpdate(EntityLiving.java:125)
at net.minecraft.entity.Entity.onUpdate(Entity.java:174)
at net.minecraft.entity.EntityLiving.onUpdate(EntityLiving.java:237)
at net.minecraft.entity.EntityMob.onUpdate(EntityMob.java:40)
at net.minecraft.world.World.updateEntityWithOptionalForce(World.java:1603)
at net.minecraft.world.World.updateEntity(World.java:1579)
at net.minecraft.world.World.updateEntities(World.java:1487)
at net.minecraft.client.Minecraft.runTick(Minecraft.java:1274)
at net.minecraft.client.Minecraft.run(Minecraft.java:555)
at java.lang.Thread.run(Unknown Source)
Save img: skins/Piffs, bytes: 398
Stopping!

SoundSystem shutting down...
Author: Paul Lamb, www.paulscode.com

Увы логи говорят за себя,если раньше было достаточно 4 перезахода,то сейчас не заходит вообще

java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Byte
at net.minecraft.src.DataWatcher.getWatchableObjectByte(DataWatcher.java:48)
at net.minecraft.entity.Entity.getEntityFlag(Entity.java:1260)
at net.minecraft.entity.Entity.isSprinting(Entity.java:1240)
at net.minecraft.entity.Entity.onEntityUpdate(Entity.java:190)
at net.minecraft.entity.EntityLiving.onEntityUpdate(EntityLiving.java:125)
at net.minecraft.entity.Entity.onUpdate(Entity.java:174)
at net.minecraft.entity.EntityLiving.onUpdate(EntityLiving.java:237)
at net.minecraft.entity.EntityMob.onUpdate(EntityMob.java:40)
at net.minecraft.world.World.updateEntityWithOptionalForce(World.java:1603)
at net.minecraft.world.World.updateEntity(World.java:1579)
at net.minecraft.world.World.updateEntities(World.java:1487)
at net.minecraft.client.Minecraft.runTick(Minecraft.java:1274)
at net.minecraft.client.Minecraft.run(Minecraft.java:555)
at java.lang.Thread.run(Unknown Source)

Раньше когда часто перезаходил этот лог исчезал,и получалось следующее :

"C:\Program Files\Java\jre6\bin\java.exe" -Xms564M -Xmx564M -jar Minecraft.jar
Heap size: 545.0
Heap is big size
run complite
16 achievements
Head acc: + 7
277 recipes
update not found: old c24a55a122eb21076c444e683320d345, new: c24a55a122eb21076c444e683320d345
replace complite

water_mode: 0
anti_aliasing: 2
reflection_resolution: 4
reflective_items: true
reflective_clouds: false
reflect_player: true
render_v3: 1.0
water_surface_transparency: 0.05
waterfall_transparency: 0.4
water_color: 0.0, 0.4, 0.3
waterfall_color: 1.0, 1.0, 1.0
waterfall_fog: true

WARNING: Found unknown Windows version: Windows 7
Attempting to use default windows plug-in.
Loading: net.java.games.input.DirectAndRawInputEnvironmentPlugin

Starting up SoundSystem...
Initializing LWJGL OpenAL
(The LWJGL binding of OpenAL. For more information, see http://www.lwjgl.org)
OpenAL initialized.

Connecting to 86.62.89.4, 130
H: LOL-ÏÊ, k: 8
Thead new download: cloaks/null
Try to load: cloaks/null
Thead new download: skins/Piffs
Thead new download: cloaks/Piffs
Try to load: skins/Piffs
Try to load: cloaks/Piffs
LOGIN PACKiffs
New max size: 324
New max size: 484
New max size: 784

Увы не знаю решение проблемы,прошу помощи...