If when using redsn0w to jailbreak your iphone you find it hangs at “uploading ramdisk” take the following steps to resolve the problem.
Close and reopen redsn0w
Before selecting your firmware open task manager and find the redsn0w.exe process. Right click this process and click Set affinity.
Uncheck CPU 0 in the Processor Affinity menu.
Carry on using redsn0w as normal and the problem should be solved!