In Helgen at the headsmans block alduin doesn't land, he just circles around the tower and the game won't progress. It has only started doing this since the newest patch. I have already tried disabling all my mods and verifying the games files and it still won't work.

List the mods you have (the actual names of the mods) and your system's specs. People can't help unless you give us both of those.

As i said, i already tried disabling all my mods and it still wouldn't work so i don't see how listing them would make any difference. but whatever.

A Quality World Map - All Roads
Alternate Pressure Plates
Better Dynamic Snow
Crime overhaul
Distant LOD Terrain Noise
Enhanced Blood Textures
Enhanced Horse Skins
Extended Colors
Full Screen Map
Giants Physics Fix
Glowing Ore Veins
Height Adjusted Races
High Res Flora
HQ Fire & Water - Stereo Sound Conversion
Immersive Thunder
Immersive Detect Life Spell
IMO Perks
Improved NPC Clothing
Killable Children
Lunar Moth Brighter
MDRT - MoreDeath Reload Time
More Colorful Butterflies
Natural nvde
Nicer Snowflakes - Realistic
No Deep Cave Ambiance Loops
Pure Flame Atronach
QD Interface
Realistic Crime Radius
Realistic Ragdoll Death Force
Reign of Fire
Remove Cairns
Retextured Wolfs & Recolored Pelts
RWT - Realistic Water Textures Full
Semi Transparent Tripwires
ShoutCD
ShoutCD - Unrelenting Force Option
SkillToOne
SKSE
SkyBoost
SkyHD
Skyrim Enhanced Shaders
Skyrim Memory 4GB Patch
Skyrim Weapon Retex Project
SkyUI
Smoke & Embers High Res
UnLeveled World
Visible Windows High
XCE - Xenius Character Enhancements

Some of them may not be exactly original names - I rename some of them if the original name is too cryptic to remember the purpose of it.

You're using mods which no longer work with the current skyrim version. (4GB, Skyboost).

I think your problem lies with that to be honest. Disabling mods does not always stop the game from seeing the files they use.

If you're using an old version of skyrim, we can't really help you.

Skyboost still works for me, when i disable it i only get about 35fps average with all the texture mods on, with it on i get a fairly steady 50.

As for the problem, i think i figured it out. I think Alduins landing in Helgen is time based rather than a consistent event. I had used the (set timescale to 1) console command right at the start of the game. I tried restarting again without using it right away and the scene triggered properly.

Well figured out mate, I'll remember that for future issues