Minecraft – I can’t log in to Minecraft please help

Have you tried looking in the event viewer after you have a lock up. To open the event viewer right click on My Computer and select Manage. Look at System Tools > Event Viewer > Application. If you double click an item in the event list it will give you a detailed description of the event.

These numbers are in bytes, add M at the end to make them megabytes.

Contrary to the popular belief, more is not always better. As always with performance optimizations you should measure first, understand the problem, and then increase JVM memory only if that is indeed the problem (and then measure yet again to check if that fixed anything). For example, look at the "Used Memory: xx%" at the top right of the F3 screen. Normal behavior is it increases for a few seconds and then drops sharply and then starts to increase again and so on. If the minimum is hovering above 75%, or the maximum consistently hits 90%+, then Java memory might be a problem.