Taping over previously recorded tape

You need to get a cleaning cassette.
Read it's instructions before using.

I've had a similar problem, the solution to mine was that one of the tape heads had moved out of position by a fraction and so it was having problems tracking back through the tape footage... if you put in a tape that you know isn't blank and press play then hold fastforward to skip through the tape can you see footage on the tape fast forwarding? If so you need an engineer to realign the tape heads for you.

If recently recorded plays back ok, and there's no warning about low rf or head clogging problems,it seems to be electronic problem in vtr board,but usually is head problem,which is not so expensive.

Video head was dirty / clogged due to old tapes usage so it did not recorded any signal on tape and now it requires cleaning with good quality head cleaning tape to record and playback properly.

I have a sony 14E and suddenly it stopped playing and recording. With vertical lines on the screen I knew to clean the heads. No effect on the recording/playing malfunction.

However I persevered and it seems to have worked in it is now recording and playing back. The steps I suggest, with PERSEVERANCE, are :
1. Clean the heads (I did it 3 times in all, with about 1 hour between each session);
2. Leave the camera open (tape section) for about 2 hours and put the camera (with or without tape) in a warm place. (I also had condensation messages).
3. Once it is warm put in a recorded tape and attempt to view it. At first I had "dirty" vertical lines for a few seconds but it cleared and played normally.
4. If Step 3 still does not work repeat 1 and 2. As I said PERSEVERE.
If Step 3 works then try to record. It should work hopefully. If not, repeat 1 and 2 (shortening the "Warm Up" time).
Good luck. I hope mine continues to work OK now. It is to do with dirty heads and coldness I think.

I have about 2 to 3 tapes that wont play on any of my cameras. I have lots of footage on each of them.

A Q-tip should never be used to clean a video head.  Unfortunately they can pull the tiny head out of alignment.  I believe this is your problem and the repaid may be more costly than a new purchase.

Im thinking your tape path is out of alignment.

Many HDV cameras and decks are able to play and record DV as well as the higher-resolution HDV format. Additionally, many of these HDV devices will attempt to automatically change their settings to match the format of the tape that it's playing. Here are some tips for using these types of devices with Final Cut Pro / Final Cut Express.
Tip: Make explicit settings on your HDV device. Instead of using an "Auto" setting, make your own settings on your HDV device to keep the communication going between it and Final Cut Pro / Final Cut Express. This also helps Final Cut Pro / Final Cut Express keep things running smoothly with HDV devices that handle both DV-NTSC and DV-PAL.
For example, say you're using an HDV deck to capture footage from a tape that was recorded as DV-NTSC. Before capturing in Final Cut Pro / Final Cut Express, make sure that you set the deck to DV mode specifically—don't rely on Auto mode. With some devices, you may need to disconnect it from FireWire to change the mode.
For a common capture workflow, this sequence of steps can provide the best results:

1. Quit Final Cut Pro / Final Cut Express if it's open.
2. Insert your tape into your HDV deck or camcorder.
3. Use the device's menus to set it to match the format that's recorded on the tape.
4. Connect your HDV device to your computer with a FireWire cable.
5. Open Final Cut Pro / Final Cut Express.
6. Choose an Easy Setup for DV or HDV (whichever matches the format recorded on your tape).
7. Proceed to Log and Capture.

Tip: Quit Final Cut Pro / Final Cut Express before changing modes. It's generally a good idea to quit Final Cut Pro / Final Cut Express before you change the mode on your device from DV to HDV, or from HDV to DV, and then re-open the application again.
Tip: Use an Easy Setup to play back non-default HDV format footage on your HDV device. You can use Final Cut Pro / Final Cut Express to make your HDV device play back footage in its non-default HDV format. For example, maybe you have a 1080i60 HDV device and want to play back footage that was recorded as 1080i50. Or perhaps you have a 1808i50 HDV device and you want to play back footage that was recorded as 1080i60. To do this, follow these steps:

1. Connect your camera to your computer.
2. In Final Cut Pro / Final Cut Express, choose an HDV preset Easy Setup that matches the format of the tape's footage (you don't need to restart Final Cut Pro / Final Cut Express).
3. Your device's LCD display should automatically display a switch to 60 or 50, indicating the type of media that's being played.

Playing back non-default DV format footage on your HDV device You can also use your HDV device to play back footage in its non-default DV format too. For example, maybe you have a 1080i60 HDV device and want to play back footage that was recorded as DV-PAL. Or maybe you have a 1080i50 HDV device and want to play back footage that was recorded as DV-NTSC. If so, follow these steps:

1. Make sure that your device is in DV/DVCAM mode.
2. Put your device into Play/Pause mode, then open the Log and Capture window in Final Cut Pro / Final Cut Express.
3. Make sure that your device's LCD (or other readout screen) displays the same format as your tape or Final Cut Pro / Final Cut Express will misinterpret what type of device you have.

Tip: Avoid recording both HDV and DV formats on the same tape. Use separate tapes whenever you want to record in a different format. If you need to record over existing footage in a different format (for example, you have a tape with DV-PAL on it, but you want to record over it with HDV 1080i50), it's a good idea to black and code the tape, or completely record over the old footage with contiguous recording in the new format. If the tape contains even a second of, say, DV in the middle of an HDV tape (or vice versa), it could cause unexpected results later when you try to capture video from that tape.
For more information, see HD and Broadcast Formats and the Final Cut Pro / Final Cut Express User Manual, available under the Final Cut Pro / Final Cut Express Help menu

You may have a problem with the image sensor device (CCD). From October 3, 2005 through October 2, 2007, Sony will repair, free of charge, affected products exhibiting the above-mentioned problem where it is caused by the image sensor device. Sony will also cover the cost of shipping and handling from and to addresses within the United States and US Territories for service to correct this issue. To see if you have this problem: Power On your camcorder (make sure the battery is fully charged). Check the LCD screen and verify that the display icons are turned on. If you cannot see the icons, press the Display button until the icons are visible. Put a tape in the camcorder. With the lens cap off, record some video. NOTE: Be sure to speak during the recording so the video will contain your voice. Rewind this section of the tape (using tape counter to verify start of your recording). Play back the recorded video and use the LCD screen on the camcorder to view it. You should hear the audio you recorded and the Display icons/text will still appear. If your camcorder is affected by this CCD issue, the picture will either be extremely distorted, or there will be no visible picture (just a blank LCD screen with the display icons still visible).