No sound from speakers. Flashing sound mode shown on one speaker faintly. powerlight is not on. Headphones sound OK.

Are the speakers selected for A or B or AB check the speakers by using a 1.5 volt batter on the cable going to the speakers, if you get a sound from the speaker, you know they are ok, if not, speakers are faulty.

If the sound is also dead on that channel on a pair of headphones. Then you have probably lost the main power amp for that channel. To be certain. With you headphones on, slide or turn the balance control so you can only hear the faulty channel. With some music playing turn up the volume. If you can hear "faintly" music playing then the pre-amp is OK and the power amp has gone.
The power amp will be located on a heat sink. It will consist of 4 transistors (2 for each channel) or one big device (or two) (an IC). If it is transistors you only need to replace the two for the right channel.

Make sure you have not put it into tape monitor mode.

Try headphones... possibly the switch contacts on the headphone jack which disconnect the speaker when headpones are plugged in. If you can hear via the headphones, check the switch contacts. Also look for a loose cable.

Contacts can oxidize when idle for a long time.

if the sound is very faint. you can check the volume properties if it is set to maximize and also check the physical volume control on the actual speaker - also Disconnect Any Headphones That May Be Connected to the Computer - Check for and remove any headphones connected to the computer or speakers to prevent them from muting the external speakers.Click Start, and then click Control Panel.Double-click Sounds and Audio Devices. Click the Sounds tab. You can also try head phone if it is Crystal Clear on headphone then the problem is with the Speaker as Dell might need to replace it. :)

If headphones work then so does the amplifier. When did this problem start? From what I can find it almost sounds like it thinks you have headphones plugged in, which would disable the speakers.

Because the sound is only faint says to me that the power amp that controls the left channel is faulty. You need to look at the device(s) on the heatsink and probably replace them.

unless you are capable of replacing the jak on the speaker u need a new pair. the wiring functions the the jack which is now broken

sounds like you may have a bad tweeter in your speaker. change the right and left speakers and see if the problem persists in that same speaker. if so, you have a bad speaker.

turn your speakers up and moisten your finger. touch the jack plug that inserts into the pc, if you hear the speakers buzz/crackle then they are ok. If not I would try a new lead if possible, else speakers are u/s as if headphones work then speakers should as well as use the same output from the pc, just amplify it unlike headphones. You could also check in the cpanel to see if your speakers are set to speakers and not headphones but to be honest I cant see this stopping the speakers altogether.