Please check that the VGA Video cable / DVI cable connection from the PC to the PC input (VGA) jack / HDMI socket on the bottom of the TV is properly secured
If the connection is good, then the problem could be due to the switching on sequence of the TV and the PC. Follow the recommended switch-on sequence:
First turn on the TV and select a TV program.
Then turn on the PC and wait till the PC boot up.
Press the 'AV+' button on the remote control to show the SOURCE list menu on the TV.
Press the cursor up/down to select PC-VGA or PC-D, depends on the connection, and press the cursor right to activate the selected mode.
Toggle the PC to transfer the signal to the TV.