The remote control has a "Game" button, which is how you select the external input. Since you don't have a remote you can select game mode via the front panel Menu button:
1) Press the MENU button so that the menu display appears on the TV screen.
2) Press the VOL(ume) ▲ button so that "PICTURE" is selected.
3) Select the feature you wish to adjust with the CH(annel) ▲ or ▼ button and adjust it with the VOL(ume) ▲ or ▼ button.
GAME MODE: Set to the most suitable position for TV
GAME. [+] : ON [ - ] : OFF
This will place your TV into Game mode and use the front panel video/audio jacks.
Here is a link to download the user guide: http://www.sylvaniaconsumerelectronics.com/support/manual/index.aspx
Just enter your model number.
Please let me know if you have any questions.