You could try to code C to ASM using a compiler directive.

Then you are able to see what the compiler generates! A debugging tool can also solve many starters problems.

#pragma src

can be used in keil...

Try first .. solid coding to see if your hardware is working fine.

main()
{
P0 = 0xaa;
while (1);
}

compile and test

main ()
{
p0 = 0x55;
while (1);
}

compile and test... this should give you some indication of the problem. In assembler pretty easy to see what happens.

the startup file clears your RAM (and initialize some registers for some CPU's).

Have fun ...