Esto es lo que indica la consola. / This is what the console indicates.

ERROR StatusLogger Unable to open jar:file:/C:/Users/Gian!/AppData/Roaming/.minecraft/libraries/org/apache/logging/log4j/log4j-core/2.8.1/log4j-core-2.8.1.jar!/META-INF/log4j-provider.properties java.io.FileNotFoundException: C:\Users\Gian (El sistema no puede encontrar el archivo especificado) at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.<init>(ZipFile.java:220) at java.util.zip.ZipFile.<init>(ZipFile.java:150) at java.util.jar.JarFile.<init>(JarFile.java:166) at java.util.jar.JarFile.<init>(JarFile.java:103) at sun.net.www.protocol.jar.URLJarFile.<init>(URLJarFile.java:93) at sun.net.www.protocol.jar.URLJarFile.getJarFile(URLJarFile.java:69) at sun.net.www.protocol.jar.JarFileFactory.get(JarFileFactory.java:94) at sun.net.www.protocol.jar.JarURLConnection.connect(JarURLConnection.java:122) at sun.net.www.protocol.jar.JarURLConnection.getInputStream(JarURLConnection.java:150) at java.net.URL.openStream(URL.java:1038) at org.apache.logging.log4j.util.ProviderUtil.loadProvider(ProviderUtil.java:79) at org.apache.logging.log4j.util.ProviderUtil.<init>(ProviderUtil.java:66) at org.apache.logging.log4j.util.ProviderUtil.lazyInit(ProviderUtil.java:124) at org.apache.logging.log4j.util.ProviderUtil.hasProviders(ProviderUtil.java:108) at org.apache.logging.log4j.LogManager.<clinit>(LogManager.java:89) at net.minecraft.client.main.Main.<clinit>(SourceFile:33) ERROR StatusLogger Log4j2 could not find a logging implementation. Please add log4j-core to the classpath. Using SimpleLogger to log to the console... Exception in thread "Client thread" java.lang.ExceptionInInitializerError at jy.<clinit>(SourceFile:20) at qv.<clinit>(SourceFile:22) at cyc.<clinit>(SourceFile:212) at net.minecraft.client.main.Main.main(SourceFile:155) Caused by: java.lang.NullPointerException at java.io.Reader.<init>(Reader.java:78) at java.io.InputStreamReader.<init>(InputStreamReader.java:113) at hy.<init>(SourceFile:32) at hy.<clinit>(SourceFile:25) ... 4 more ERROR Main Caught previously unhandled exception : java.lang.NoClassDefFoundError: Could not initialize class cyc at net.minecraft.client.main.Main$2.run(SourceFile:138)