My Aspire won't load up

When I turn it on it beeps 2 times , then the 1st screen come up where it tells me to press F1 to resume then it goes to a screen that says :

Intel UNDI, PXE-2.0 (build 082)

Copyright (c) 1997-2000 Intel Corporation

For Realtex RTL8139(X)/8130/810X PCI Fast Ethernet Controller v2.13 (020326)

PXE-E61: Media text failure, cable check

PXE-MOF: Exiting PXE ROM.

Then it goes black for 20 sec then the 2nd screen pops up and it keeps just repeatedly doing that over and over again.

Don't know what to do please help.