General :: Make Install Error With Created Makefile

I am new to Linux and I am trying to install a C program from source using Makefile. So I 've created a "hello world" program and then a Makefile to install it. Then I logged in as root and used
make install

The following error occurs:
make: execvp: /usr/bin: Permission denied
make: *** [install] Error 127

Here is the Makefile:
CC=gcc
CFLAGS=-c -Wall
PROGS = hello
INSTDIR = $(prefix)/usr/bin/
INSTMODE = 0755
INSTOWNER = root
INSTGROUP = root

all: $(PROGS)
$(PROGS): main.o
$(CC) main.o
main.o: main.c
$(CC) $(CFLAGS) main.c
install:$(PROGS)
$(INSTALL) $(INSTDIR)
$(INSTALL) $(INSTMODE) $(INSTOWNER) -o $(INSTGROUP) $(PROGS) $(INSTDIR)
clean:
rm -rf $(PROGS) *o $(PROGS)
So, where are the errors