Your disply refresh rate is set too high which is not supported by your monito.
(i) Press F8 during boot to invoke the startup menu and select safemode to start with.
(ii) Right click on desktop , go to display properties, --> Click Advanced-->Click Adaptor/Monitor -->Change the refresh rate from 'Unknown' to 'Adapter default'.
(iii) Set uour resolution to 640 X 480, 16 Color mode, ClickOK to Windows warning.
(iv) Reboot the system (in normal mode). Set the color & resolution to 640 X480 , High Color. Go through anothereboot.
(v) After restart you can increase the resolution & refresh rate in small steps if required.
