Pc not sending signal to monitor

[skymode]

hello,
my monitor is not reciving singals from pc when i unplug the vga cable from behind the pc the monitor starts (saying not connected to pc) but when i plug it back again the monitor's light start's blinking and it does not start any possible solution why it is happening?

Extra- it happened when is installed new windows xp with sp3

 

[hytecgowthaman]

system information ?
reinsert gpu in other slot. update bios and firmwares.

 

[skymode]

my specs are
4gb DDR 3 ram
Intel dual core processor
150gb hardrive