Learn Hardcore Turkish: Teknisyen modemi yeniden başlatıyor. - The technician is restarting the modem.

It’s the present continuous: başlat- + -(I)yor → başlatıyor = “is restarting.” It usually means the action is happening now or around now. It can also be used for near-future plans: Yarın modemi yeniden başlatıyorum = “I’m restarting the modem tomorrow.” For general/habitual facts you’d use the aorist: Modemi sık sık yeniden başlatır = “(He/She) often restarts the modem.”

Why is it modemi and not just modem?

Because -i marks the definite direct object (accusative). Modemi = “the modem (object).” The vowel is i (not ı/u/ü) due to 4-way vowel harmony: the last vowel in modem is front and unrounded (e), so choose i.

Can I drop the -i and say modem instead?

You can, but it changes the meaning:

Teknisyen modemi yeniden başlatıyor = “The technician is restarting the modem” (a specific, known modem).
Teknisyen modem yeniden başlatıyor = “The technician is restarting a modem” (indefinite/generic). More natural with an explicit article: Bir teknisyen bir modem yeniden başlatıyor = “A technician is restarting a modem.”

Where does yeniden go, and does moving it change anything?

Adverbs like yeniden typically come before the verb. The element right before the verb is in focus. So:

Teknisyen modemi yeniden başlatıyor (focus on “again,” i.e., it’s a restart).
Modemi teknisyen yeniden başlatıyor (emphasizes that it’s the technician, not someone else). Other orders are possible for emphasis, but the given sentence is the neutral/default.

What’s the difference between yeniden, tekrar, and yine for “again”?

yeniden = “anew/over again,” very common with processes/devices; default for “restart” in tech.
tekrar = “again/one more time”; also fine with başlatmak: tekrar başlatmak.
yine = “again” (and “still” in some contexts); yine başlatıyor emphasizes repetition (“is doing it again”), but for “restart” as a technical action, yeniden is safest.

Why başlatmak and not başlamak?

başlamak is intransitive (“to begin” by itself). başlatmak is transitive/causative (“to make something begin; to start something”). Here, the technician causes the modem to start: Teknisyen modemi başlatıyor. The causative suffix is -t: başla- → başlat-.

How would I say “The modem is being restarted” (passive)?

Use the passive: Modem yeniden başlatılıyor.

How do I pronounce başlatıyor and where is the stress?

ş = “sh”
ı (dotless i) = a close back unrounded vowel, like the “a” in “sofa” when unstressed.
Stress in the -(I)yor progressive is on the syllable before -yor: baş-la-TI-yor.

Why is it spelled başlatıyor and not başlatiyor?

The progressive suffix is harmonized as -(I)yor. After a back unrounded vowel like a, it becomes -ıyor. So: başlat- + -ıyor → başlatıyor (not “-iyor”).

Could modemi mean “his/her modem” here?

Not in object position. “His/her modem” as a direct object would be modemini (possessive + accusative): Teknisyen modemini yeniden başlatıyor = “The technician is restarting his/her modem.” In your sentence, modemi is just the definite object “the modem.”

Do I need an apostrophe in modemi?

No. Apostrophes are only for proper names with suffixes (e.g., Ahmet’i). Common nouns take suffixes without an apostrophe: modemi, bilgisayarı, telefonu.

How would I negate or ask a question with this sentence?

Negative: Teknisyen modemi yeniden başlatmıyor = “The technician is not restarting the modem.”
Yes–no question: Teknisyen modemi yeniden başlatıyor mu? = “Is the technician restarting the modem?”

How does the verb change with different subjects?

Present continuous of başlatmak:

Ben: başlatıyorum
Sen: başlatıyorsun
O: başlatıyor
Biz: başlatıyoruz
Siz: başlatıyorsunuz
Onlar: başlatıyor(lar) (-(l)ar is optional in speech)

Is resetlemek or sıfırlamak the same as “restart”?

Not exactly.

yeniden başlatmak = restart/reboot (turn off and on again).
resetlemek (loanword) / sıfırlamak = reset to factory settings (erases configuration). In everyday talk some people say modemi resetlemek when they mean “restart,” but technically it’s different.