If the car has hydractive suspension it will have a slide switch to the left of the gear lever, to switch between Normal and Sport modes.
There will also abe a zig-zag light in the main instrumants binnacle that should illuminate for 3 seconds on Ign on. This lamp, top left of instruments, should also light when the switch is slid to Sport mode..
You won't be able to see the extra sphere under front of the car, but a quick check is to see if the front corner spheres are fed by either 3.5mm pipes, or 10mm pipes. Hydractive uses 10mm pipes, standard suspension are 3.5mm.
I would be surprised if a 2.5td Exclusive doesn't have Hydractive.
As far as you fault goes, it could be as already said, a sphere has ruptured, but it could be an electrical issue keeping the suspension locked in hard mode.
The only way to fully check spheres is with a pressure tester, alternatively fit new ones.
Member Gasa has a very nicely made one, which He made from a bottle jack. See post
viewtopic.php?f=7&t=10339&p=123764#p123764
Start the engine and bounce both the front and rear of the car, then switch off, close the doors and tailgate, wait one minute and try bouncing again.
The car should feel much stiffer for the second test, as it should now be in firm mode.
Being a Series 2 Xm, it will have Hydractive 2 (assuming it has hydractive).
Hydractive 2 systems are susceptible to the diodes in the electrovalves failing due to heat, which stops the hydractive system functioning and can damage the Ecu output mosfets.
Install additional protection diodes into the wiring loom near the Hydractive Ecu. If the system has shut down it may come back to life, but is good preventative maintenance anyway.
The interior lights issue may be the long timer relay (837), which is mounted under the glovebox, but it's possible the interior lights issue, computer resetting and Hydractive issue (if fitted and the problem is electrical), are linked.
Check all power and Gnd feed are in good condition, pay particular attention to the Gnd point on the right inner wing near the Ecu box and the battery clamps and leads, especially the negative lead where it fits into the battery clamp.
Note: The interior lights and trip computer are both fed from F27 and both use Gnd point m5, which is under the steering column.
To check the interior light function press the interior lights button on the dashboard and watch the indicator light in the switch. If the indicator lamp fails to illuminate, or flickers, suspect the relay has failed. The switch feeds power to the relay, which feeds it back to the switch tell-tale and interior lights.
Please see attached, Gabor's excellent XM Series-2 circuit diagrams from the Self help files. to check the wiring and for diode installation.
download/file.php?id=9711
Appologies for the long post, but we need you to start investigating and reporting back so we can narrow down the actual causes of your faults.
There is no reason to be nervous about an Xm, all faults are fixable with a bit of thought.
Rust is the killer of Xm and you car appears in very good condition in that respect.
Hopefully someone will have an owners handbook for you, but in the meantime the fuses are listed in the circuit diagrams.