Generally speaking, what's in your truobleshooting toolbox for hardware related problems?
Think multimeters, memtest86 and other things, but not wireshark and disassemblers
Typically, swapping out known good parts. I dont have much equipment that i have the knowledge to test with a multimeter. The going philosophy at my place of business is always have one spare, so nearly always theres an identical part that we are pretty confident works.
I recently found a cat5 tester invaluable for testing and identifying fault in a vertical run, and really how else would you do that? two multimeters and a couple radios?
Software-wise UBCD isnt bad. Nearly any linux livecd or USB distro can be made to test hardware effectively, as there are a multitude of tools for that in the repos for most distributions.
If a hard drive is questionable but still works (and it sata or pata) i usually rip it out and either image it or just copy off the necessary data using a USB drive sled. Then it can typically be tested/fixed/identified as bad using that machines disk tools.
I have a vendor support contract, and a well-stocked on-site spares pile. Sure, I've got multimeters, oscilloscopes, soldering stations and all manner of weird shit at home, but on the job it's far more efficient and makes far more business sense just to swap parts (whole systems, if I'm not sure what might be the cause of the problem) to get things up and running, then validate the failure and ship the busted stuff back to the vendor.
If I have the parts the old parts swapping technique is used. I also have a commercial product called MicroScope, which is a bootable CD with a large range of testing software that can be run in a number of ways, including batch mode for testing multiple devices. I usually set that up at the end of the day and let it run overnight. My copy of MicroScope is getting a bit old now and I need to get an update, if there is one, because it sometimes doesn't test very recent hardware.
I know memtest86 has a lot of fans but I no longer use it since discovering that it isn't too reliable. I've had several occasions where memtest86 said the RAM was OK when it wasn't. MicroScope does of course include RAM testing.
For cable testing, in me previous position I used a superb device from Fluke (expensive!) but I now use a simple CAT/Phone cable tester that I purchased at a local electronics supplier for about $20. It reports continuity and cable sequence with a set of 9 LEDs.
I have a foam hammer that I use. But it tends to work better on the users than the hardware.
Seriously I always keep a Linux live cd such as System Recovery CD. I've found that Linux tends to give better hardware errors and it takes the installed OS out of the picture.
I also keep a spinrite cd with me to deal with low level hard drive issues.
I'm a management dope now whose only tool is a blackberry, but when I cared about servers, my top tools were:
Our servers could be at any of 500 locations or 6 datacenters, so screwdrivers aren't very useful :)
A selection (not all of then all the time ) and many are as much for routine hardware removal/insertion and changing ... and don't use them unless you are competent to tackle what you're about to do and (where appropriate) trained, qualified, authorised and have the time and conditions to do the work safely:
Small Phillips head and flat head screwdrivers
'pearl catcher' for retrieving the small screw when I drop it (I find the '4-wire' version easier than the '3-wire' for small objects)
spanner and large screwdriver for equipment rack bolts
Ethernet cable tester to check wiring (e.g. normal, xover, faulty)
multimeter (continuity tests, low tension voltage checks)
thermocouple or (preferably) laser/infrared temperature measurement device
room thermometer / humidity meter
radio clock (for accurately setting and checking time)
pen and paper
back in the days of serial connections: break-out boxes and oscilloscope
cutters for removing cable ties
tweezers/forceps for setting DIP switches and handling header plugs
spare screws, bolts, thumbscrews for computer cases, cable ties, DIP headers
temporary cable labels
tape measure (metric, imperial, U)
bags to hold removed bolts, screws &c
small cleaning kit