Here's the Vostro 230
Service Manual. Give that a good read before you do anything else. Id suggest you first unplug the PSU powercord from the wall outlet then hold down the power button for 15 seconds to bleed off any residual current in the mobo.
Remove the case cover and then remove the CMOS battery for 3 minutes (this clears the CMOS and returns the BIOS to all default settings). While you're in there disconnect, inspect then reconnect all wiring connectors, and be sure that memory modules and graphics card (if any) are properly seated.
Reinstall the CMOS battery and plug the PSU back in. Start the computer and immediately enter the BIOS setup (press the F2 key at the Dell logo boot screen) and make sure that the date/time are set correctly, and that the boot order is set to CDROM first and HDD second. Save and exit BIOS to test if it will boot into Windows. If you still get the blinking cursor then (as has already been noted) there's no operating system installed.
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