Ok, i have installed mods successfully ever sense i've had it, i know very well how to install mods, now to the point.I have all updated mods, using modloader, I deleted the META-INF file, Copy and pasted all class files in to minecraft.jar, as a test i ran minecraft, clicked log in, it black screen shortly after. It has done this multiple times, I've done this with other mods as well. Side note i did this after a force update.
Many mods aren't yet updated for 1.5.2 -- are you using outdated mods? Also, was a crash report generated? If so, post it in a spoiler.
If you want to use mods that are currently incompatible, you may want to downgrade to 1.5.1 and install them from there. Grab the old JAR from http://assets.minecraft.net/1_5_1/minecraft.jar
If you want to use mods that are currently incompatible, you may want to downgrade to 1.5.1 and install them from there. Grab the old JAR from http://assets.minecraft.net/1_5_1/minecraft.jar
Stu