In order to make my book more palatable, I want to know if there is a scenario where all surface radio communication could be permanently blocked, either by technological or natural phenomena, so that the only communication would be over shielded coaxial cables?
It depends on your definition of "blocked," and your definition of "all." For nearly every real radio transmission, and important factor is Signal to Noise Ratio. If the signal is too weak compared to the noise, it's hard to make anything out. You could have a very powerful noise source in the atmosphere wrecking all communications by raising the noise floor to an unacceptable level.
It would still theoretically be possible to get a signal through by supplying more power. However, in practice this is not always a solution. Power costs money, and more powerful RF hardware costs money too.
Another approach would be the one Countto10 mentioned in comments. If you fill the air with small particles, they act like antennas which messes up signal propagation. This is the idea behind chaff, which is used as a radar-countermeasure that makes it hard to see your aircraft:
The limit of this approach is that these materials resonate most on specific frequencies. That's why you see different cut lengths of chaff -- to target different frequencies. In theory you could have a fractaline material that resonates on many frequencies, but it gets tricky. It also gets tricky for low frequencies. The lower the frequency, the longer the antenna must be (or the more complex the fractal).
One thing to be careful of when blocking RF is that there's nothing differentiating RF from visible light other than frequency. If you come up with too good of a way to block RF, you might have accidentally found a way to block visible light as well, which is likely not part of your plan.
You could try either jamming, blocking or "dissuading".
jamming: you need a very powerful radio noise source covering all frequencies. Possibly ionization in the stratosphere, or an overwhelming radio source. You could posit a stellar jet resonating in the radio range, and "spraying" the volume of space through which the Solar System travels in its orbit in the galaxy.
There recently has been somewhat of a scare due to the fact that a runaway Wolf-Rayet star, WR-104, about 8000 lyrs way out Sagittarius, was believed to be preparing to "point" its gamma maser at Earth. Apparently it isn't... perhaps. However, a radio burst is always possible, and some of them have the energy of half a billion suns. Even if they're very far, they are loud.
For short periods, coronal mass ejections should do fine.
With a considerable amount of handwaving, you could have an impossibly advanced "solar satellite" in L1 orbit accidentally generating and focusing a permanent, small solar storm on itself. The plasma cocoon makes it impossible to communicate with the satellite to change things, and the backlash is injected in Earth's stratosphere, supercharging it with ionized particles. Short range communications, especially at night, should still be possible, but unreliable (at some point Bruce Willis ought to try and reach the satellite somehow to disable it, though).
blocking: a very strong ionizing radiation source could make the atmosphere ionized, and radio reflectant. Only in the directly exposed area (the half of the Earth facing the emitter, which would need to be of stellar power) and also causing an ecological catastrophe, sterilizing most of surface life and probably boiling the atmosphere off.
A technological kind of jamming could be obtained using self-replicating, sun-powered nanodroids transmitting white noise.
Passive radio-opaque floating nanodroids are also "possible", for unlikely values of possible: you'd need so many that they'd block sunlight (another ecological catastrophe ensues) and they'd need to be correctly spaced at the right distances to cover all useable frequencies.
Other possibilities include orbiting weapon platform equipped with ARM missiles, kinetic impactors, or lasers. Radio communication is possible in theory, but in practice any attempt at unshielded transmission ends in a large boom.
(And then there's Fred Hoyle's Black Cloud).
The issue with blocking "everything" is the inverse-squares law. If the target system is for transmitting signals one mile, then to block it from a distance of ten miles needs not ten times its power, but a hundred. You can reduce that using a directional antenna if you know where your target is, but this is not blocking everything everywhere at once. On top of this military radio uses all sorts of tricks to avoid being jammed, or even detected.
Of course, there is the EMP option. A few big nukes at high altitude will "block" almost all radio equipment across hundreds of miles radius by burning it out. It will do the same to the power grid, so that is pretty much curtains for technological civilisation if the attack is worldwide. A rather drastic form of "blocking". Military hardened systems and "antique" civilian kit using only thermionic valves will probably survive until there is no way left to charge the batteries.
Summary: you are unlikely to be able to block all short-range radio systems at long range, or all mil-spec radio systems at all.
A strong solar storm can cause massive interference in radio communication, and even in unprotected conductive cables (like power lines). It would also fry all but the sturdiest receivers. A solar storm wouldn't block very strong signals, but would make it highly impractical to transmit signals via radio rather than over insulated cables.
Another issue is that such a storm is, at least for our sun, not permanent. There are stars out there with stronger solar storms. I don't know if there are stars with continuous solar storms.