Troubleshooting

Prints fail. That's normal — even experienced owners get failures. Nearly every failure is one of the handful below. Match the symptom, try the fix, change one thing at a time.

First layer won't stick

The most common failure. The plastic curls up or drags behind the nozzle instead of lying flat.

Bed isn't clean. Fingerprints kill adhesion. Wash with soap and water, then wipe with isopropyl alcohol.
Nozzle gap wrong (mostly older printers — modern ones set this automatically). Too high and plastic can't grip; re-do the paper-drag test from Your First Print.
Bed too cool. Make sure it's actually reaching the filament's bed temperature (60°C for PLA).
Drafts. A breeze across the bed (AC vent, open window) cools the plastic mid-layer. Shield the printer or move it.

Stringing (thin hairs between parts)

The nozzle oozes while traveling. Usually temperature or retraction:

Drop nozzle temperature 5–10°C.
Check that retraction is enabled in the slicer (it pulls filament back during travel moves).
Damp filament also strings — dry the spool if stringing appears suddenly on a previously fine setup.

Layer shifts (print suddenly offsets sideways)

Something moved that shouldn't have:

Loose belts are the usual cause — re-tension them.
Something blocking the print head's path (a curled-up print, a tool left on the frame).
Printing far too fast for the printer's mechanics.

Clogged nozzle (thin or no extrusion)

Do a cold pull: heat the nozzle, push filament in, cool to ~90°C, then yank it out — it drags debris with it.
If that fails, swap the nozzle. Nozzles are cheap wear items; don't mourn them.

Warping (corners lift off the bed)

The plastic shrinks as it cools and pulls the corners up. Common with ABS/ASA, rare with PLA:

Enclosure or at least draft protection.
Brim for more grip area.
Right bed temperature for the filament.

Spaghetti (a bird's nest of plastic)

The print detached mid-print and the nozzle kept extruding into air. Cause is usually one of the adhesion issues above — the spaghetti is the symptom, not the disease. Clean up, fix adhesion, reprint.

When to stop and ask

If the same failure survives three rounds of fixes, stop changing settings and get a second pair of eyes: a photo on r/3Dprinting or a maker forum, with your printer model, filament type, and temperatures. "PLA, 200/60, first layer won't stick" gets useful answers; "printer broken pls help" doesn't.