If, for any reason, your Microsoft Windows system does not have any C: drive (aka volume), then Xilinx ISE 13.1 will not start. Unless you apply the following trick...

Let's assume you installed Xilinx ISE 13.1 on drive H:. Then edit line number 8 of the following file:

H:\Xilinx\13.1\ISE_DS\SysGen\.settings32.bat

original row:

set TEMP=C:\TEMP

changed row:

set TEMP=H:\TEMP

Enjoy.